U.S. patent application number 15/242188 was filed with the patent office on 2018-02-22 for methods and system for engine control.
The applicant listed for this patent is Ford Global Technologies, LLC. Invention is credited to Kenneth John Behr, Mark Thomas Linenberg, Adithya Pravarun Re Ranga, Ethan D. Sanborn, Gopichandra Surnilla, Joseph Lyle Thomas.
Application Number | 20180051647 15/242188 |
Document ID | / |
Family ID | 61082768 |
Filed Date | 2018-02-22 |
United States Patent
Application |
20180051647 |
Kind Code |
A1 |
Ranga; Adithya Pravarun Re ;
et al. |
February 22, 2018 |
METHODS AND SYSTEM FOR ENGINE CONTROL
Abstract
Systems and methods for determining air-fuel error in an engine
fueled via direct and port fuel injection. Errors associated with
individual fuel injection systems are distinguished from a common
error based on trends in the error correction coefficients of the
individual fuel injection systems. Adaptive fuel multipliers for
each injection system are updated to account for the common
error.
Inventors: |
Ranga; Adithya Pravarun Re;
(Canton, MI) ; Surnilla; Gopichandra; (West
Bloomfield, MI) ; Thomas; Joseph Lyle; (Kimball,
MI) ; Sanborn; Ethan D.; (Saline, MI) ;
Linenberg; Mark Thomas; (Howell, MI) ; Behr; Kenneth
John; (Farmington Hills, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ford Global Technologies, LLC |
Dearborn |
MI |
US |
|
|
Family ID: |
61082768 |
Appl. No.: |
15/242188 |
Filed: |
August 19, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02D 41/1454 20130101;
F02D 41/3094 20130101; F02D 41/2467 20130101; F02D 2041/389
20130101; F02D 35/0092 20130101; F02D 41/26 20130101; F02D 41/402
20130101 |
International
Class: |
F02D 41/40 20060101
F02D041/40; F02D 35/00 20060101 F02D035/00; F02D 41/26 20060101
F02D041/26; F02D 41/14 20060101 F02D041/14 |
Claims
1. A method for fueling a cylinder, comprising: injecting fuel to
the cylinder via a first fuel injector and a second fuel injector;
and distinguishing an error associated with the first fuel injector
or the second fuel injector from a common fuel system error as a
function of a rate of change of air-fuel ratio error and a fraction
of fuel injected via the first fuel injector or the second fuel
injector.
2. The method of claim 1, wherein the common fuel system error
includes one or more of an airflow error associated with an airflow
path delivering air to both the first fuel injector and the second
fuel injector, and a fuel-type error associated with the fuel
injected by both the first fuel injector and the second fuel
injector.
3. The method of claim 1, where estimating as a function of the
air-fuel ratio error and the fraction includes: dividing a rate of
change of air-fuel ratio error by the fraction of fuel injected via
the first fuel injector to determine a first slope; dividing the
rate of change of air-fuel ratio error by the fraction of fuel
injected via the second fuel injector to determine a second slope;
and if the first slope is within a threshold difference of the
second slope, and each of the first and second slope is higher than
a threshold value, learning a minimum of the first and second slope
as the common error.
4. The method of claim 1, wherein correcting each of the first and
second error based on the common error includes: determining a
correction factor based on the common error; and reducing each of
the first and the second error by applying the correction
factor.
5. The method of claim 4, further comprising: adjusting a transfer
function of the first fuel injector with the reduced first error;
adjusting a transfer function of the second fuel injector with the
reduced second error; and adjusting fueling of the cylinder using
the adjusted transfer function of the first and the second fuel
injector.
6. The method of claim 3, wherein the estimating further includes:
if the first slope is not within the threshold difference of the
second slope, learning the air-fuel ratio error as the error
associated with the first fuel injector when the first slope is
higher than the threshold value; and learning the air-fuel ratio
error as the error associated with the second fuel injector when
the second slope is higher than the threshold value.
7. The method of claim 4, further comprising, comparing the reduced
first error with the reduced second error; deactivating the first
injector when the first error is larger and fueling the engine with
the second fuel injector; and deactivating the second injector when
the second error is larger and fueling the engine with the first
fuel injector.
8. The method of claim 1, wherein the injecting is performed in
each of a plurality of engine air mass flow regions and wherein
each of the first, second, and common error are learned in each of
the plurality of engine air mass flow regions as a function of air
mass flow.
9. The method of claim 1, where the first fuel injector is a direct
fuel injector and where the second fuel injector is a port fuel
injector.
10. A method for an engine fuel system, comprising: injecting fuel
to an engine cylinder via a first fuel injector and a second fuel
injector during a cylinder cycle, the first and second fuel
injector having distinct types of fuel injection; assigning a first
portion of an air-fuel error from the cylinder during the cylinder
cycle to a first error associated with the first fuel injector;
assigning a second portion of the air-fuel error to a second error
associated with the second fuel injector; and assigning a third
portion of the air-fuel error to a common error associated with the
fuel system, wherein each of the first, second, and third portion
is based on each of a first fuel fraction provided by the first
fuel injector, a second fuel fraction provided by the second fuel
injector, and the air-fuel error.
11. The method of claim 10, wherein the assigning includes:
learning a first rate of change in the air-fuel error with a change
in the first fuel fraction; learning a second rate of change in the
air-fuel error with a change in the second fuel fraction; and if
the first rate is within a threshold difference of the second rate,
and each of the first and second rate are higher than a threshold,
assigning a minimum of the first rate and the second rate to the
common error.
12. The method of claim 11, wherein the assigning further includes:
if the first rate is outside the threshold difference of the second
rate while the first and the second are higher than the threshold,
assigning the first portion based on the first fuel fraction
provided by the first fuel injector; and assigning the second
portion based on the second fuel fraction provided by the second
fuel injector.
13. The method of claim 10, further comprising: assigning a first
adaptive fuel multiplier corresponding to the first error to the
first fuel injector; assigning a second adaptive fuel multiplier
corresponding to the second error to the second fuel injector;
updating each of the first and second adaptive fuel multiplier with
a correction factor based on the common error; and adjusting
fueling of the engine with each of the updated first and second
adaptive fuel multipliers.
14. The method of claim 11, further comprising: limiting operation
of the first fuel injector in response to the first portion of the
air-fuel error being greater than the second portion; and limiting
operation of the second fuel injector in response to the second
portion of the air-fuel error being greater than the first
portion.
15. The method of claim 14, wherein limiting operation of the first
fuel injector includes fueling the engine via only the second
injector and wherein limiting operation of the second fuel injector
includes fueling the engine via only the first injector.
16. The method of claim 10, wherein each of the first, second, and
third portion are learned as a function of air mass flow.
17. An engine system, comprising: an engine including a cylinder; a
port fuel injector in fluidic communication with the cylinder; a
direct fuel injector in fluidic communication with the cylinder; an
exhaust air-fuel ratio sensor; and a controller including
executable instructions stored in non-transitory memory for: while
operating the engine with closed loop air-fuel ratio control based
on feedback from the air-fuel ratio sensor, updating an adaptive
fuel multiplier for each of the port and the direct injector with a
correction factor based on a common error in airflow to both the
port and the direct injector, the common error estimated based on a
ratio of a change in air-fuel error to a change in fuel fraction
from the port and the direct injector during engine fueling; and
adjusting fueling via one or more of the port and direct fuel
injection using the adaptive fuel multipliers.
18. The system of claim 17, wherein the adaptive fuel multiplier
for the port injector is based on a first ratio of the change in
air-fuel error to the change in fuel fraction from the port
injector, wherein the adaptive fuel multiplier for the direct
injector is based on a second ratio of the change in air-fuel error
to the change in fuel fraction from the direct injector, wherein
the common error is based on a minimum of the first and the second
ratio when the first and the second ratio are within a threshold of
each other, and wherein the updating includes reducing the adaptive
fuel multiplier for each of the port and the direct injector.
19. The system of claim 17, further comprising: indicating
degradation of the port fuel injector when the adjusted adaptive
fuel multiplier for the port injector is higher than a threshold;
indicating degradation of the direct fuel injector when the
adjusted adaptive fuel multiplier for the fuel injector is higher
than the threshold; and indicating engine fueling error due to the
common error when the adjusted adaptive fuel multiplier for each of
the port and the direct injector have a common directionality and
each adjusted adaptive fuel multiplier is higher than the
threshold.
20. The system of claim 19, wherein the air-fuel error is based on
a difference between a commanded air-fuel ratio and an actual
air-fuel ratio estimated by the air-fuel ratio sensor, and wherein
the adjusting the fueling includes: updating the adapted fuel
multiplier commanded to the direct fuel injector while disabling
the port injector responsive to degradation of the port fuel
injector; and updating the adapted fuel multiplier commanded to the
port fuel injector while disabling the direct injector responsive
to degradation of the direct fuel injector.
Description
FIELD
[0001] The present description relates to systems and methods for
determining fuel injector error in an internal combustion
engine.
BACKGROUND/SUMMARY
[0002] Dual fueling engine systems with direct and port fuel
injectors may be configured to operate under a wide range of engine
operating conditions. For example, at higher engine speeds and
loads, fuel may be directly injected into engine cylinders to
increase engine torque and enhance cooling of cylinder charge
mixtures while minimizing chances of engine knock. At lower engine
speeds and loads, fuel may be injected via port fuel injection to
reduce particulate matter emissions. Specifically, port injected
fuel may quickly evaporate as fuel is drawn into an engine
cylinder, reducing particulate matter buildup while improving fuel
efficiency. Fuel may be injected into an engine via both direct and
port fuel injection during mid-speeds and loads in order to improve
combustion stability and reduce engine emissions. Therefore, an
engine with direct injectors (DI) and port fuel injectors (PFI) can
leverage the advantages of each individual injection type.
[0003] While it may be beneficial to incorporate port and direct
fuel injectors into an engine, supplying fuel via two different
injection systems may make it difficult to distinguish injection
errors resulting from the port injector from those resulting from
the direct injector. One example approach for determining which
fuel injection source is introducing fueling errors into the engine
is shown by Surnilla et al in US20160131072. Therein, port and
direct fuel injector errors are determined by calculating a ratio
of a change in fuel multiplier values and a change in fraction of
fuel injected into engine via port and direct injection, wherein
fuel multiplier values are determined based on a measured air-fuel
ratio. A port injector error is determined by calculating a ratio
of a change in fuel multiplier values and a change in fraction of
port injected fuel, and a direct injector error is determined by
calculating a ratio of change in fuel multiplier values and a
change in fraction of directly injected fuel.
[0004] However the inventors herein have identified potential
issues with such a system. As one example, the approach is not able
to distinguish fueling errors of direct and port fuel injectors
from a common error. As such, an air-fuel ratio error in an engine
may have an error contribution from one or more of the direct
injector, the port injector, and the common error. The common error
may include a common fuel type error and/or an air error. A common
fuel type error may occur when a quality of a fuel being injected
into the engine degrades. For example, changes in fuel viscosity
may cause both port and direct fuel injectors to provide a lower or
a larger fuel amount than expected, causing a common fuel type
error. Alternatively, a common fuel type error may occur when the
actual fuel injected into engine is different from the expected
fuel, such as when the oxygen content of a fuel injected into a
flex fuel engine deviates from the oxygen content of the fuel
refilled into the fuel tank. Further still, the common error may be
an air error caused by a degraded engine sensor such as mass air
flow sensor, a pressure sensor or a throttle position sensor.
Alternatively, an air error in a multi-cylinder engine may occur if
some engine cylinders receive more air than other cylinders due to
location of the cylinders along an intake air passage or due to a
configuration of the intake passage.
[0005] Discrepancies in learning air-fuel error in an engine fueled
via both direct and port fuel injection may occur when direct and
port fuel injector errors are determined without accounting for the
common error. For example, a common error in an engine may be
misdiagnosed as both a direct and port fuel injector error, with
the adaptive fuel multiplier (or transfer functions) for both
injectors being affected. As such, this can result in
overcompensation for the error. For example, an engine controller
may identify the error as a direct injector error or a port
injector error and may correct for the error by adjusting a
transfer function of the corresponding injector, and disabling the
degraded injector. However, if the air-fuel error is due, at least
in part, to a common error, the air-fuel error may persist even
after the transfer function of a fuel injector is adjusted. In
addition, the common error may cause a fuel injector to appear
degraded. The controller may disable the fuel injector responsive
to the incorrect indication of degradation, as a result of which
the advantages of that particular injection type may not be
leveraged.
[0006] In one example, the issues described above may be addressed
by a method comprising: fueling a cylinder via a first and a second
fuel injector; estimating each of a first injection error of the
first injector, a second injection error of the second injector,
and a common error as a function of an air-fuel ratio error and a
fraction of fuel injected via each of the first and second
injector; and correcting each of the first and second error based
on the common error. By separating individual error contributions
of each of a direct fuel injector and a port fuel injector from the
common error, air-fuel errors may be better compensated for.
Overall, engine performance and exhaust emissions are improved.
[0007] For example, a total air-fuel error may be determined in an
engine fueled with both direct and port fuel injectors as a
difference between an actual air-fuel ratio (determined at an
exhaust gas sensor) and an expected air-fuel ratio. A portion of
that error that is due to a fueling error of the direct fuel
injector may be determined as a function of the rate of change in
the air-fuel ratio error relative to a rate of change in the
fraction of the total fuel injected via direct injection. Likewise,
a portion of that error that is due to a fueling error of the port
fuel injector may be determined as a function of a rate of change
in the air-fuel ratio error relative to a rate of change in the
fraction of the total fuel injected via port injection. If the
ratios for both the port and direct injectors change by a small
magnitude during engine operation but the air-fuel errors
corresponding to different engine speed-load conditions are higher
than a threshold air-fuel error and have a common directionality
(that is, both the port and the direct injector are either
indicating a rich air-fuel error or a lean air-fuel error), then a
portion of the error may be attributed to the common error. The
common error may be learned as a minimum of the two ratios. The
controller may then adjust the transfer function of each injector
taking into account the common error. For example, the common error
contribution may be removed during the transfer function
adjustment. As a result, common error may be differentiated from
fuel injector errors and accordingly compensated for.
[0008] The approach described here may confer several advantages.
In particular, the approach allows errors that are common to both
fueling systems to be distinguished from fueling errors of
individual direct and port fuel injectors. Further, the common
errors may be compensated for when adjusting the transfer function
of direct and port fuel injectors for their individual errors. By
separating individual fueling errors of the direct and port fuel
injectors from the common error, air-fuel imbalances generated by
overcompensation or under-compensation of fuel injector errors can
be reduced. Further, the approach may reduce the erroneous
disabling of non-degraded fuel injectors.
[0009] It should be understood that the summary above is provided
to introduce in simplified form a selection of concepts that are
further described in the detailed description. It is not meant to
identify key or essential features of the claimed subject matter,
the scope of which is defined uniquely by the claims that follow
the detailed description. Furthermore, the claimed subject matter
is not limited to implementations that solve any disadvantages
noted above or in any part of this disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is an illustration of an engine with a cylinder.
[0011] FIG. 2A shows an example table of adapted fuel
multipliers.
[0012] FIG. 2B shows an example graphical output for determining
fueling errors of a direct and port fuel injector.
[0013] FIG. 2C shows an example table of adapted fuel multipliers
used to determine a common error in an engine operating different
speeds and loads.
[0014] FIG. 2D shows an example graphical output for determining a
common error in the engine.
[0015] FIG. 3 shows a flowchart for determining fuel injector error
and common error in an engine with direct and port fuel
injectors.
[0016] FIG. 4 shows an example graphical output for determining
fueling error contributions from direct and port fuel
injectors.
[0017] FIG. 5 shows an alternative method for determining direct
and port fuel injector error, and common error in an engine.
[0018] FIG. 6 shows an example graphical output for separating
fueling error of direct and port fuel injectors from a common
error.
DETAILED DESCRIPTION
[0019] The following description relates to systems and methods for
determining air-fuel errors in an internal combustion engine with
cylinders fueled by direct and port fuel injection. FIG. 1 depicts
an engine cylinder fueled via direct and port fuel injection. FIG.
2A shows an example table of adapted fuel multiplier values. The
adapted fuel multipliers may be used to indicate air-fuel error in
an engine with direct and port fuel injectors. FIG. 2B shows an
example graphical output for determining direct and port fuel
injector error as a ratio of change in adapted fuel multiplier
values relative to fraction of fuel injected via direct and port
fuel injection, respectively. FIG. 2C shows an example table of
adapted fuel multipliers used to determine a common error in an
engine operating different speeds and loads. The common error may
be indicated if values of the adapted fuel multipliers exceed a
stoichiometric value of 1.0. FIG. 2D shows an example graphical
output for determining a common error in the engine. An absolute
slope of adapted fuel multipliers and fraction of fuel injected via
direct and port fuel injectors indicates a magnitude of the common
error. An engine controller may be configured to perform a control
routine, such as the example routine of FIG. 3, to learn and
distinguish a fuel injector error from a common error in the system
of FIG. 1. FIG. 4 shows an example graphical output for
distinguishing and correcting for a common error. FIG. 5 shows a
method for determining individual contributions to an overall
fueling error from each of a direct and port fuel injector, and a
common error. An example graphical output for distinguishing and
compensation for individual contributions is shown in FIG. 6.
[0020] Referring to FIG. 1, internal combustion engine 10,
comprising a plurality of cylinders, one cylinder of which is shown
in FIG. 1, may be controlled by electronic engine controller 12.
Engine 10 includes combustion chamber 30 and cylinder walls 32 with
piston 36 positioned therein and connected to crankshaft 40.
Flywheel 97 and ring gear 99 are coupled to crankshaft 40. Starter
96 includes pinion shaft 98 and pinion gear 95. Pinion shaft 98 may
selectively advance pinion gear 95 to engage ring gear 99. Starter
96 may be directly mounted to the front of the engine or the rear
of the engine. In some examples, starter 96 may selectively supply
torque to crankshaft 40 via a belt or chain. In one example,
starter 96 may be in a base state when not engaged to the engine
crankshaft. Combustion chamber 30 is shown communicating with
intake manifold 44 and exhaust manifold 48 via respective intake
valve 52 and exhaust valve 54. Each intake and exhaust valve may be
operated by an intake cam 51 and an exhaust cam 53. The position of
intake cam 51 may be determined by intake cam sensor 55. The
position of exhaust cam 53 may be determined by exhaust cam sensor
57.
[0021] Direct fuel injector 66 is shown positioned to inject fuel
directly into cylinder 30, which is known to those skilled in the
art as direct injection. Port fuel injector 67, injects fuel to
intake port 69, which is known to those skilled in the art as port
injection. Fuel injector 66 delivers liquid fuel in proportion to a
pulse width of a signal from controller 12. Likewise, fuel injector
67 delivers liquid fuel in proportion to a pulse width from
controller 12. Fuel is delivered to fuel injectors 66 and 67 by a
fuel system (not shown) including a fuel tank, fuel pump, and fuel
rail (not shown). Fuel may be supplied to direct fuel injector 66
at a higher pressure while fuel may be supplied to port fuel
injector 67 at a lower pressure. In addition, intake manifold 44
may communicate with optional electronic throttle 62 which adjusts
a position of throttle plate 64 to control air flow from air intake
42 to intake manifold 44. In some examples, throttle 62 and
throttle plate 64 may be positioned between intake valve 52 and
intake manifold 44 such that throttle 62 is a port throttle.
[0022] Engine 10 of FIG. 1 may be fueled with different types of
fuel. For example, engine 10 may be capable of using gasoline,
diesel, ethanol, methanol, a mixture of gasoline and ethanol (e.g.,
E85 which is approximately 85% ethanol and 15% gasoline), a mixture
of gasoline and methanol (e.g., M85 which is approximately 85%
methanol and 15% gas), etc. In another example, engine 10 may use
one fuel or fuel blend (e.g., gasoline or gasoline and ethanol) and
one mixture of water and fuel (e.g., water and methanol). In yet
another example, engine 10 may use gasoline and a reformate fuel
generated in a reformer coupled to the engine.
[0023] Direct and port fuel injector fueling errors may occur in an
engine operating under a wide range of conditions. Fuel injector
fueling errors may result from clogged fuel injectors, a faulted
fuel metering device, a degraded fuel injector pump, etc. Further,
a common error which includes a common fuel type error and air
error may also occur in an engine fueled via both direct and port
fuel injection. The common error represents an air error or a
fueling error that is observable simultaneously in both types of
injectors as a fuel injector error, the error in both injectors
occurring to the same degree and with the same directionality. A
common fuel type error may occur due to degraded fuel, for example,
and may cause both port and direct fuel injectors to provide a
lower or larger fuel amount than expected. For example, if the
viscosity of a fuel changes, the fuel injectors may inject a
different amount of fuel than expected causing a fueling error. In
another example, a common fuel type error may occur when the actual
fuel injected into an engine is different from the expected fuel,
such as when the oxygen content of a fuel injected into a flex fuel
engine deviates from the oxygen content of the fuel refilled into
the fuel tank. In one example, a fuel tank may be refilled with E10
and E10 is expected to be injected into the engine. However, due to
the fuel tank being previously filled with E50, and a small amount
of E50 remaining in the fuel tank when the fuel tank was refilled
with E10, the final composition of fuel injected into the engine
may have an alcohol content (and therefore an oxygen content) that
is higher than E10. This can result in a common fuel-type error. A
common air error, on the other hand, may occur due to a degraded
engine sensor such as a mass air flow sensor, a pressure sensor or
a throttle position sensor. Alternatively, a common air error may
occur if some engine cylinders receive more air than other
cylinders due to the particular location of the cylinders along an
intake air passage, or due to the configuration of the intake
manifold (e.g., the passage, the plenum, the runners, etc.). As
elaborated at FIGS. 3-4, the engine controller may learn a fueling
error and determine whether the fueling error is due to a direct
injector fueling error, a port injector fueling error, or a common
error. As elaborated at FIGS. 5-6, the engine controller may learn
a fueling error and determine which portion of the fueling error is
due to the direct injector fueling error, the port injector fueling
error, and the common error. In each case, the common error may be
differentiated based on a ratio of a rate of change of air-fuel
error relative to a rate of change of a fraction of directly
injected fuel, as well as a rate of change of a fraction of port
injected fuel. In response to the different errors, distinct
mitigating actions and transfer function compensations may be
performed to enable the engine to be operated at a desired air-fuel
ratio.
[0024] Distributorless ignition system 88 provides an ignition
spark to combustion chamber 30 via spark plug 92 in response to
controller 12. Universal Exhaust Gas Oxygen (UEGO) sensor 126 may
be coupled to exhaust manifold 48 upstream of catalytic converter
70. Alternatively, a two-state exhaust gas oxygen sensor may be
substituted for UEGO sensor 126.
[0025] In one example, the catalytic converter 70 may include
multiple catalyst bricks. In another example, multiple emission
control devices, each with multiple bricks, may be used. In yet
another example, the catalytic converter 70 may be a three-way type
catalyst.
[0026] Controller 12 is shown in FIG. 1 as a conventional
microcomputer including: microprocessor unit 102, input/output
ports 104, read-only memory (ROM) 106 (e.g., non-transitory
memory), random access memory (RAM) 108, keep alive memory (KAM)
110, and a conventional data bus. Controller 12 may receive various
signals from sensors coupled to engine 10, in addition to those
signals previously discussed, including: engine coolant temperature
(ECT) from temperature sensor 112; an accelerator pedal position
signal from position sensor 134 coupled to accelerator pedal 130
operated by input 132; a brake pedal position signal from pedal
position sensor 154 coupled to brake pedal 150 operated by input
152, engine manifold pressure (MAP) from pressure sensor 122; an
engine position signal from Hall effect sensor 118 coupled to
crankshaft 40; air mass entering the engine from sensor 120; and
throttle position signal from sensor 58. Barometric pressure may
also be sensed (sensor not shown) for processing by controller 12.
In a preferred aspect of the present description, engine position
sensor 118 produces a predetermined number of equally spaced pulses
every revolution of the crankshaft from which engine speed (RPM)
may be determined. The controller 12 receives signals from the
various sensors of FIG. 1 and employs the various actuators of FIG.
1 to adjust engine operation based on the received signals and
instructions stored on a memory of the controller. For example,
based on input from an exhaust gas sensor regarding an air-fuel
ratio error, the controller may adjust a fuel multiplier for each
fuel injector, and accordingly send an adjusted signal to a driver
for each fuel injector to update a fuel injection pulse-width for
each fuel injector.
[0027] In some examples, the engine may be coupled to an electric
motor/battery system in a hybrid vehicle. Further, in some
examples, other engine configurations may be employed, for example
a diesel engine with multiple fuel injectors. Further, controller
12 may communicate conditions such as degradation of engine
components to display panel 171.
[0028] During operation, each cylinder within engine 10 typically
undergoes a four stroke cycle: the cycle includes the intake
stroke, compression stroke, expansion stroke, and exhaust stroke.
During the intake stroke, generally, the exhaust valve 54 closes
and intake valve 52 opens. Air is introduced into combustion
chamber 30 via intake manifold 44, and piston 36 moves to the
bottom of the cylinder so as to increase the volume within
combustion chamber 30. The position at which piston 36 is near the
bottom of the cylinder and at the end of its stroke (e.g., when
combustion chamber 30 is at its largest volume) is typically
referred to by those of skill in the art as bottom dead center
(BDC). During the compression stroke, intake valve 52 and exhaust
valve 54 are closed. Piston 36 moves toward the cylinder head so as
to compress the air within combustion chamber 30. The point at
which piston 36 is at the end of its stroke and closest to the
cylinder head (e.g., when combustion chamber 30 is at its smallest
volume) is typically referred to by those of skill in the art as
top dead center (TDC). In a process hereinafter referred to as
injection, fuel is introduced into the combustion chamber. In a
process hereinafter referred to as ignition, the injected fuel is
ignited by known ignition means such as spark plug 92, resulting in
combustion. During the expansion stroke, the expanding gases push
piston 36 back to BDC. Crankshaft 40 converts piston movement into
a rotational torque of the rotary shaft. Finally, during the
exhaust stroke, the exhaust valve 54 opens to release the combusted
air-fuel mixture to exhaust manifold 48 and the piston returns to
TDC. Note that the above is shown merely as an example, and that
intake and exhaust valve opening and/or closing timings may vary,
such as to provide positive or negative valve overlap, late intake
valve closing, or various other examples.
[0029] In this way, the system of FIG. 1 provides for a system,
comprising: an engine including a cylinder; a port fuel injector in
fluidic communication with a cylinder; a direct fuel injector in
fluidic communication with the cylinder; an exhaust air-fuel ratio
sensor; and a controller including executable instructions stored
in non-transitory memory for: while operating the engine with
closed loop air-fuel ratio control based on feedback from the
air-fuel ratio sensor, differentiating an engine fueling error due
to degradation of one or more of the port and the direct fuel
injector from an engine fueling error due to a common error in
airflow to both the port and the direct fuel injector based on a
ratio of a change in air-fuel error to a change in fuel fraction
from the port and the direct injector during engine fueling; and
adjusting fueling via one or more of the port and direct fuel
injection responsive to the differentiating.
[0030] The system of FIG. 1 also provides for a system comprising:
an engine including a cylinder; a port fuel injector in fluidic
communication with the cylinder; a direct fuel injector in fluidic
communication with the cylinder; an exhaust air-fuel ratio sensor;
and a controller including executable instructions stored in
non-transitory memory for: while operating the engine with closed
loop air-fuel ratio control based on feedback from the air-fuel
ratio sensor, updating an adaptive fuel multiplier for each of the
port and the direct injector with a correction factor based on a
common error in airflow to both the port and the direct injector,
the common error estimated based on a ratio of a change in air-fuel
error to a change in fuel fraction from the port and the direct
injector during engine fueling; and adjusting fueling via one or
more of the port and direct fuel injection using the adaptive fuel
multipliers.
[0031] Referring to FIG. 2A, an example table is shown with a
plurality of adapted fuel multipliers determined at different
engine loads and speed. The adapted fuel multiplier values may be
used to indicate air-fuel error in an engine operating under a wide
range of conditions. The example values of the adapted fuel
multipliers depicted in Table 200 may be used to adjust fuel
supplied to the engine as shown by equation below.
M fuel = M air Kamrf AF stoich Lam ( Eq . 1 ) ##EQU00001##
where M.sub.fuel is mass of fuel delivered to the engine, is mass
of air inducted to engine, Kamrf is an adapted fuel multiplier
value, .DELTA.F.sub.stoich is a stoichiometric air-fuel ratio and
Lam is a fuel correction parameter based on a measured air fuel
error.
[0032] The horizontal axis in Table 200 represents engine speed,
and engine speed increases from left to right. The vertical axis
represents engine load, and engine load increases in the direction
of the vertical axis. The horizontal axis in Table 200 partitions
the table vertically into a plurality of cells that may be indexed
via engine speed while the vertical axis partitions the table
horizontally into the plurality of cells that may be indexed based
on engine load. When the engine is operating nominally with no
air-fuel error, Table 200 may be populated with unit values of
adapted fuel multiplier which may be updated based on feedback from
an exhaust gas sensor (such as exhaust sensor 126 at FIG. 1). The
values of the adapted fuel multipliers may be updated based on a
difference between an actual air-fuel ratio determined at the
exhaust sensor and an expected air-fuel ratio. After updating the
values of the adapted fuel multipliers, the updated values may be
used to determine the amount of fuel delivered to engine cylinders.
For example, the engine may be operating with an engine load of 0.3
and engine speed of 500 rpm. From Table 200, an adapted fuel
multiplier value (corresponding to an engine load of 0.3 and speed
of 500 rpm) may change from an initial value of 1.0 to 0.75. An
engine air-fuel error of 0.25 (1.0-0.75) may be determined based on
the above values of fuel multipliers. The air-fuel error of 0.25
may indicate a rich air-fuel variation. In an alternative example,
an engine may be operating with a load of 0.8 and speed of 4000
rpm. From Table 200, an adapted fuel multiplier value
(corresponding to an engine load of 0.8 and speed of 4000 rpm) may
change from an initial value of 1.0 to 1.15. An engine air-fuel
error of 0.15 (1.15-1.0) may be determined based on the above
values of the selected fuel multipliers. The air-fuel error of 0.15
may indicate a lean air-fuel variation.
[0033] Referring now to FIG. 2B, an example graphical output is
shown for determining fueling errors in an engine fueled via both
direct and port fuel injection. The first plot shows adapted fuel
multiplier values and fraction of directly injected fuel used to
determine a direct injector error. The horizontal axis of the first
plot represents a fraction of fuel injected into the engine via
direct injection (DI). The fraction of directly injected fuel may
vary from 0 (e.g., no directly injected fuel) to 1.0 (e.g., all
fuel is directly injected). The second plot shows values of adapted
fuel multiplier and fraction of port injected fuel used to
determine a port fuel injector error. The horizontal axis of the
second plot represents a fraction of port injected fuel (PFI). The
fraction of fuel injected into engine via a port fuel injector may
vary from 0 (e.g., no port injected fuel) to 1.0 (e.g., all fuel is
port injected). The vertical axes of each plot represent values of
adapted fuel multiplier (Kamrf), and Kamrf increases in a direction
of each vertical axis.
[0034] In one example, an engine may initially operate at a speed
of 2000 rpm and load of 0.4. From Table 200, an adapted fuel
multiplier value corresponding to the engine speed of 2000 rpm and
engine of load 0.4 may be determined as 0.90. After a given
duration, the engine speed may increase to 5000 rpm and engine load
may increase to 0.8, the corresponding fuel multiplier may reach a
value of 1.20. As illustrated in the first plot, a fraction of
directly injected fuel during the operating period may change from
0.75 to 0.50 as depicted by line 220 and corresponding values of
the adapted fuel multiplier (Kamrf) may change from 1.2 to 0.9 as
depicted by line 222. A slope 224 of the adapted fuel multiplier
and fraction of directly injected fuel may be calculated to
determine a direct injector error. Slope 224 may be determined as a
ratio of change in Kamrf to a change in fraction of directly
injected fuel to provide a value of 1.2 ((0.9-1.2)/(0.50-0.75)).
The calculated DI slope may be compared to a threshold slope to
determine if one or more direct injectors may be degraded. If the
slope determined above is greater than the threshold slope, one or
more direct injectors may be malfunctioning. For example, a
threshold slope may be determined to be 1.15, but the calculated
slope may be 1.2, then one or more direct injectors may be degraded
since the calculated slope is greater than the threshold slope.
Consequently, degradation of one or more direct fuel injectors may
be indicated and a transfer function of the direct fuel injector
may be adjusted to correct the fueling error.
[0035] Referring to the second plot, a fraction of fuel injected
into the engine via a port fuel injector (under similar engine
operating conditions as described in the first plot) may change
from 0.25 to 0.50 as depicted by line 226 and corresponding values
of adapted fuel multiplier may change from 1.2 to 0.9 as depicted
by line 228. Slope 230 of adapted fuel multiplier values and
fraction of port injected fuel may be calculated to determine a
port injector error. Slope 230 may be determined as ratio of a
change in Kamrf to a change in fraction of port injected fuel to
provide a value of -1.2 ((0.9-1.2)/(0.50-0.25)). The calculated PFI
slope may be compared to a threshold slope to determine if one or
more port fuel injectors may be degraded. For example, the
calculated absolute PFI slope may be 1.2 but a threshold slope may
be determined to be 1.1, then one or more port fuel injectors may
be degraded since the calculated slope is greater than the
threshold slope. Consequently, degradation of one or more port fuel
injectors may be indicated and a transfer function of the port fuel
injector may be adjusted to compensate for the fueling error.
[0036] As shown in the above example, the slopes indicating error
in the direct injectors and port fuel injectors are similar and
higher than the threshold value, but with opposite directionality.
In this case, the DI fueling system may be faulted rich and the PFI
fueling system may be faulted lean. Alternatively, the DI fueling
system may be faulted lean and the PFI fueling system may be
faulted rich. The engine may be operated continuously at different
speed-load conditions, and the DI slope may be determined as a
ratio of change in the air-fuel error and change in the DI fuel
fraction. Similarly, the PFI slope may be determined as a ratio of
change in the air-fuel error and change in the PFI fuel fraction.
Subsequently, values of the DI and PFI slopes may be used to slowly
adapt or estimate each DI and PFI error, respectively, during
engine operation.
[0037] Further, the slope of adapted fuel multiplier values and
fraction of directly injected fuel may be compared with the slope
of adapted fuel multiplier values and fraction of port injected
fuel to determine if a common error is present. If the calculated
DI and PFI error slopes are substantially equal, that is both
injectors have a rich error or a lean error simultaneously, then a
common error may be present as disclosed further with reference to
FIGS. 2C-2D.
[0038] For example, an engine may be fueled by injecting fuel to a
cylinder via a first fuel injector providing a first injection type
(such as direct injection) and a second fuel injector providing a
second injection type (such as pot injection). An engine controller
may determine an air-fuel error based on a deviation of an actual
exhaust air-fuel ratio (as estimated by an exhaust gas sensor) from
an expected (or commanded) exhaust air-fuel ratio. The controller
may then determine if the error is associated with the first fuel
injector, the second fuel injector, or a common fuel system error
as a function of a rate of change of the air-fuel ratio error
relative to a fraction of fuel injected via the first fuel injector
or the second fuel injector. The distinguishing the error
associated with the first fuel injector or the second fuel injector
from the common error may include the controller adapting the
change of the air-fuel ratio error as a function of change in
fraction of fuel injected via the first fuel injector to determine
a first fueling slope error correction factor for the direct
injector, while adapting the change of air-fuel ratio error as a
function of change in fraction of fuel injected via the second fuel
injector to determine a second fueling slope error correction
factor for the port injector. If the first fuel slope error
correction factor is higher than a threshold factor, it may be
determined that the air-fuel error is due to a fueling error of the
direct injector. If the second fuel slope error correction factor
is higher than a threshold factor (e.g., the same threshold or a
different threshold), it may be determined that the air-fuel error
is due to a fueling error of the port injector. If both the port
and direct injector errors are higher than the corresponding
thresholds, and are directionally similar (i.e., either indicating
a rich or lean correction in both the DI and PFI fueling systems),
the controller may learn the air-fuel ratio error as the common
error.
[0039] In still other examples, a portion of the total error may be
learned as the common error if both the DI error and the PFI error
are higher than a threshold and are faulted in the same direction
(with the same slope). Therein the minimum of the two may be
learned as the common error and individual contributions of the DI
error and the PFI error to the total error may be accordingly
learned and accounted for.
[0040] Referring to FIG. 2C, an example table 201 is shown with a
plurality of adapted fuel multipliers determined at different
engine load-speed conditions. The multiplier values in Table 201
exceed a stoichiometric multiplier value of 1.0, which may indicate
presence of a common error. For example, an engine may operate at a
speed of 5000 rpm and load of 0.8. An adapted fuel multiplier value
corresponding to the engine speed of 5000 rpm and engine of load
0.8 may be determined from Table 201 as 1.25. In one example, fuel
multipliers values exceeding a threshold value of 1.2 may indicate
presence of a common error. Since the fuel multiplier value of 1.25
determined above exceeds the threshold value of 1.2, a common error
may be present.
[0041] Turning now to FIG. 2D, an example graphical output is shown
for determining a common error in an engine fueled via both direct
and port fuel injection. The first plot shows adapted fuel
multiplier values and DI fuel fraction used to determine the direct
injector error. The horizontal axis of the first plot represents
the fraction of fuel injected into the engine via direct injection.
The fraction of directly injected fuel may vary from 0 (e.g., no
directly injected fuel) to 1.0 (e.g., all fuel is directly
injected). The second plot shows values of adapted fuel multiplier
and fraction of port injected fuel used to determine a port fuel
injector error. The horizontal axis of the second plot represents a
fraction of port injected fuel (PFI). The fraction of fuel injected
into engine via a port fuel injector may vary from 0 (e.g., no port
injected fuel) to 1.0 (e.g., all fuel is port injected). The
vertical axes of each plot represent values of adapted fuel
multiplier (Kamrf), and Kamrf increases in a direction of each
vertical axis.
[0042] For example, an engine may initially operate at a speed of
5000 rpm and load of 0.8. An adapted fuel multiplier value
corresponding to the engine speed of 5000 rpm and engine of load
0.8 may be determined from Table 201 as 1.25. After a given
duration, the engine speed may decrease from 5000 rpm to 2000 rpm
and engine load may decrease from 0.8 to 0.3, and the corresponding
fuel multiplier may decrease from 1.25 to 1.23 as shown in Table
201. In one example, fuel multipliers exceeding a threshold of 1.2
may indicate presence of a common error.
[0043] As illustrated in the first plot, a fraction of directly
injected fuel during the operating period may change from 0.95 to
0.50 as depicted by line 232 and corresponding values of the
adapted fuel multiplier (Kamrf) may change from 1.25 to 1.23 as
depicted by line 234. A slope 236 of the adapted fuel multiplier
values and fraction of directly injected fuel may be calculated.
Slope 236 may be determined as a ratio of change in Kamrf to a
change in fraction of directly injected fuel to provide a value of
0.04 ((1.23-1.25)/(0.50-0.95)). Since both fuel multiplier values
are above the fuel multiplier threshold of 1.2, a common error may
be deemed present. Further, the calculated absolute DI slope may be
compared to an absolute PFI slope to determine a magnitude of the
common error as disclosed below.
[0044] Referring to the second plot, a fraction of fuel injected
into the engine via a port fuel injector (under similar engine
operating conditions as described in the first plot) may change
from 0.05 to 0.50 as depicted by line 238 and corresponding values
of adapted fuel multiplier may change from 1.25 to 1.23 as depicted
by line 240. Slope 242 of adapted fuel multiplier values and
fraction of port injected fuel may be determined as ratio of a
change in Kamrf to a change in fraction of port injected fuel to
provide a value of -0.04 ((1.23-1.25)/(0.50-0.05)). The calculated
absolute PFI slope may be compared to the absolute DI slope to
determine the magnitude of the common error. For example, the
calculated absolute PFI slope and DI slope are both equal to 0.04,
indicating a common error of 0.04. Consequently, degradation of one
or more direct and port fuel injectors may be indicated and
transfer functions of both the direct and port fuel injectors may
be adjusted to compensate for the common error. After the common
error is identified, the fuel multipliers may be adjusted with a
common error based correction factor.
[0045] Referring to FIG. 3, an example method 300 is shown for
determining fueling errors in an engine with direct and port fuel
injectors. The method enables an air-fuel error to be attributed to
a direct injector or a port injector or a common error.
Accordingly, distinct mitigating actions may be undertaken. A
direct injector fuel error may be determined based on a first fuel
slope correction factor determined based on a rate of change of
adapted fuel multiplier values and fraction of fuel injected via
direct fuel injection. A port fuel injector error may be determined
based on a second fuel slope correction factor determined based on
a rate of change of adapted fuel multiplier values and fraction of
fuel injected via port fuel injection. By comparing the first and
the second fuel slope correction factor, DI and PFI errors may be
distinguished from a common error. Instructions for carrying out
method 300 and the rest of the methods included herein may be
executed by a controller based on instructions stored on a memory
of the controller and in conjunction with signals received from
sensors of the engine system, such as the sensors and output
described above with reference to FIG. 1. The controller may employ
engine actuators of the engine system to adjust engine operation,
according to the methods described below.
[0046] At 302, an engine is operated in closed loop air-fuel
control mode. During closed loop air-fuel control, a controller
(such as controller 12 of FIG. 1) determines a desired engine
air-fuel ratio by indexing tables and/or functions based on driver
demanded torque, engine speed, engine load, and other engine
operating conditions. Fuel may be injected into the engine via
direct and/or port fuel injectors to provide the desired engine
air-fuel ratio, and feedback from an exhaust gas sensor (such as
exhaust gas sensor 126 at FIG. 1) may be used to adjust the amount
of fuel injected. A fraction of fuel injected via the direct and
port fuel injectors may also be determined based on engine load and
speed, such as by indexing a look-up table. As an example, at lower
engine speeds and loads, a larger portion of the total fuel amount
may be delivered via port injection. As another example, at higher
engine speeds and loads, a larger portion of the total fuel amount
may be delivered via direct injection.
[0047] Next at 304, method 300 adapts a value of a fuel multiplier
based on sensor readings at the exhaust gas sensor. The exhaust gas
sensor may indicate a lean or rich air-fuel ratio depending on
engine operating conditions. Specifically, if the exhaust gas
sensor indicates a lean or rich air-fuel error over a duration
greater than a threshold duration, an adapted fuel multiplier may
be incremented or decremented from an initial unit value to a new
reading based on a magnitude of air-fuel error measured at the
exhaust gas sensor. The threshold duration may be determined based
on a number of times fuel multiplier values have been adjusted.
Alternatively, the threshold duration may be determined during the
adaptive learning based on a difference between a current fuel
multiplier and a previous fuel multiplier exceeding a threshold
difference. The adapted fuel multiplier values may be learned at a
plurality of engine speeds and loads, and at a plurality of engine
air masses/mass flows, and stored in a memory of the engine
controller. In addition, the fractions of fuel injected via direct
and port fuel injectors, and the corresponding adapted fuel
multiplier values and engine load-speed may be stored in the memory
of the controller. After learning and adjusting fuel multiplier
values at different engine speeds and loads, the routine proceeds
to 306.
[0048] At 306, it may be determined if adaptive learning of fuel
multiplier values has reached a mature learning limit. Learning
maturity may be based on a number of times adapted fuel multiplier
values have been updated. Alternatively, the mature learning limit
may be reached if a difference between a current value and previous
value of a fuel multiplier is larger than the threshold difference.
Furthermore, the routine may determine if a sufficient number of
adapted fuel multiplier values and corresponding fuel fractions
injected via direct and port fuel injectors have been stored in the
memory of the controller. If the adapting learning has reached the
mature learning limit, the routine proceeds to 308. Otherwise, if
the adapting learning has not matured, the routine proceeds to 310
to continue monitoring air-fuel ratio errors and fuel fault
conditions.
[0049] Next at 308, the routine determines if any of the adapted
fuel multiplier values are out of range. If the answer is YES,
method 300 proceeds to 312. Otherwise, the answer is NO and the
routine exits and no further adjustments are performed to the
adaptive fuel multipliers. Next at 312, a slope of an adapted fuel
multiplier and fraction of directly injected fuel may be determined
at different engine loads and speeds. An engine may be operating
with both direct and port fuel injectors providing fuel to the
engine. Alternatively, the engine may be fueled via only direct
fuel injection. For example, fuel may be injected in an engine via
both direct and port fuel injectors when the engine is operating at
mid-speed and load. In another example, the engine may be fueled
via only direct injection when the engine is operating at high
engine speed and load. An example slope is illustrated at FIG. 2B,
where a slope of adapted fuel multiplier values and fraction of
directly injected fuel is determined for an engine operating at
speeds in a range of 2000-5000 rpm and engine loads in a range of
0.4-0.8. The slope of the adapted fuel multiplier values and
fraction of directly injected fuel may be determined as:
Kamrf DI = d ( Kamrf ) d ( DI frac ) ( Eq . 2 ) ##EQU00002##
where Kamrf.sub.DI is a slope of the adapted fuel multiplier values
and fraction of the directly injected fuel, Kamrf is the adapted
fuel multiplier, DI.sub.frac is the fraction of directly injected
fuel. A fuel slope correction factor for the direct fuel injector
may be adaptively learned using the following equation:
Kamrf.sub.DI-new=Kamrf.sub.DI-old+.alpha..sub.1[d(kamrf)] (Eq.
3)
where Kamrf.sub.DI-new is an updated slope of the fuel multiplier
values and DI fuel fraction, Kamrf.sub.DI-old is a previous slope
of the fuel multiplier values and DI fuel fraction, and
.alpha..sub.1 is a first gain value whose magnitude is a function
of DI fuel fraction.
[0050] At 314, the routine determines a slope of an adapted fuel
multiplier and fraction of port injected fuel at different engine
loads and speeds. For example, both direct and port fuel injectors
may be providing fuel to an engine operating at mid-speed and load.
In an alternative example, an engine may be fueled via only port
fuel injection when the engine is operating at low engine speed and
load. An example slope is illustrated at FIG. 2B, where a slope of
adapted fuel multiplier values and fraction of port injected fuel
is determined for an engine operating at speeds in a range of
2000-5000 rpm and engine loads in a range of 0.4-0.8. The slope of
the adapted fuel multiplier values and fraction of port injected
fuel may be determined as:
Kamrf PFI = d ( Kamrf ) d ( PFI frac ) ( Eq . 4 ) ##EQU00003##
where Kamrf.sub.PFI is the slope of the adapted fuel multiplier
values and fraction of the port injected fuel and PFI.sub.frac is
the fraction of port injected fuel. A fuel slope correction factor
for port fuel injector may be adaptively learned using the
following equation:
Kamrf.sub.PFI-new=Kamrf.sub.PFI-old+.alpha..sub.2[d(kamrf)] (Eq.
5)
where Kamrf.sub.PFI-new is an updated slope of the fuel multiplier
values and PFI fuel fraction, Kamrf.sub.PFI-old is a previous slope
of the fuel multiplier values and PFI fuel fraction, and
.alpha..sub.2 is a second gain value whose magnitude is a function
of PFI fuel fraction.
[0051] At 316, the routine determines if the slope of the adapted
fuel multiplier values and fraction of directly injected fuel
(Kamrf.sub.DI) is greater than a first threshold fueling slope
error. The first threshold slope error may be based on a maximum
rich or lean air-fuel ratio less than an air-fuel ratio value based
on fuel emissions standard. Alternatively, it may be determined if
an error correction coefficient for the direct fuel injection is
higher than a first threshold slope. If the calculated slope is
greater than the first threshold slope (or the error correction
coefficient for DI is higher than the first threshold slope), the
routine proceeds to 318. At 318, method 300 determines that the
fueling error is due to a direct injector error. Further, a fueling
error of one or more direct fuel injectors is determined by
comparing the calculated DI slope with the first threshold slope.
As an example, if the DI slope is 1.3, it may be determined that a
more than 30% of rich correction is being applied for the DI
fueling. Accordingly, it may be inferred that the DI fuel system is
faulted lean. As another example, if the DI slope is 0.75, it may
be determined that a more than 25% of lean correction is being
applied for the DI fueling. Accordingly, it may be inferred that
the DI fuel system is faulted rich.
[0052] In one example, the calculated DI slope may be determined as
1.4 but the first threshold slope may be determined as 1.15. Since,
the calculated DI slope is greater than the threshold slope, one or
more direct fuel injectors may be determined to be degraded. A
look-up table in the engine controller's memory may be updated to
record and store the magnitude of the direct injector error and
identity of the degraded direct fuel injectors.
[0053] Next at 320, the routine updates a transfer function of the
degraded direct fuel injectors to compensate for the DI error
determined at 318. In one example, updating the DI transfer
function may involve providing less or more fuel via direct
injection depending on a magnitude and direction of the DI error.
For example, if the DI error is determined to be a rich error, the
DI transfer function may be updated to provide a leaner DI fuel
injection. In an alternative example, updating the DI transfer
function may involve adjusting a direct injector timing and
duration depending on the magnitude and direction of the DI error.
For example, if the DI error is determined to be a rich error, the
DI transfer function may be updated to direct inject fuel earlier
and/or for a shorter duration.
[0054] Returning to 316, if the slope of the adapted fuel
multiplier values and fraction of directly injected fuel
(Kamrf.sub.DI) is less than the first threshold slope, it may be
determined that the error is not due a direct injector fueling
error and the routine proceeds to 322. At 322, the routine
determines if the slope of the fuel multiplier values and fraction
of port injected fuel (Kamrf.sub.PFI) is greater than a second
threshold slope. Alternatively, it may be determined if an error
correction coefficient for the port fuel injection is higher than a
second threshold. The second threshold slope may be based on the
maximum rich or lean air-fuel ratio less than an air-fuel ratio
value based on fuel emissions standard. The second threshold slope
may be the same as the first threshold slope. Alternatively, they
may be distinct. If the calculated PFI slope is greater than the
second threshold slope (or the error correction coefficient is
higher than the second threshold), the routine proceeds to 324. At
324, it may be determined that the fueling error is due to a port
injector error. Further, a fueling error of one or more port fuel
injectors may be determined by comparing the calculated PFI slope
with the second threshold slope. As an example, if the PFI slope is
1.3, it may be determined that a more than 30% of rich correction
is being applied for the PFI fueling. Accordingly, it may be
inferred that the PFI fuel system is faulted lean. As another
example, if the PFI slope is 0.75, it may be determined that a more
than 25% of lean correction is being applied for the PFI fueling.
Accordingly, it may be inferred that the PFI fuel system is faulted
rich. For example, a calculated PFI slope may be determined as 1.2
but the second threshold slope may be determined as 1.1. Since, the
calculated PFI slope is greater than the second threshold slope,
one or more port fuel injectors may be determined to be degraded.
After determining the PFI error, method 300 proceeds to 326.
[0055] At 326, the routine updates a transfer function of the
degraded port fuel injectors to compensate for PFI error determined
in 324. For example, updating the PFI transfer function may involve
providing less or more fuel via port fuel injectors (depending on
the magnitude and direction of the fueling error) to compensate for
the PFI error. For example, if the PFI error is determined to be a
rich error, the PFI transfer function may be updated to provide a
leaner port fuel injection. Alternatively, updating the PFI
transfer function may involve adjusting a port fuel injector timing
and duration of the timing depending on the magnitude and direction
of the PFI error. For example, if the PFI error is determined to be
a rich error, the PFI transfer function may be updated to port
inject fuel earlier and/or for a shorter duration.
[0056] Returning to 322, if the slope of the adapted fuel
multiplier values and fraction of port injected fuel
(Kamrf.sub.PFI) is less than the second threshold slope, the
routine proceeds to 328. Herein, it is determined that the air-fuel
error is not due to a fueling error of the port injector or the
direct injector. At 328, it may be determined if the slope of
adapted fuel multiplier values and fraction of directly injected
fuel (Kamrf.sub.DI) is equal to the slope of adapted fuel
multiplier values and fraction of port injected fuel
(Kamrf.sub.PFI). Alternatively, it may be determined if the error
correction coefficients for both the DI and the PFI system have the
same directionality (or sign). In one example, both slopes may be
equal and/or both error correction coefficients may have the same
directionality if the error for both the DI and the PFI system are
rich (or both lean) over a range of air masses. That is, both fuel
systems err the same way (with rich or lean) under the same
operating condition. If both slopes are equal (i.e., Kamrf.sub.DI
is equal to Kamrf.sub.PFI), or both error correction coefficients
have a common directionality, the routine proceeds to 330. At 330,
method 300 determines that the air-fuel error is due to a common
error in the engine system, such as a common fuel type error or an
air measurement error. The common error may then be determined as a
minimum of the DI error and the PFI error. For example, the common
error, Kamrf.sub.CE may be determined as:
Kamrf.sub.CE=min{(1-kamrf.sub.DI),(1-Kamrf.sub.PFI)} (Eq. 6)
[0057] For example, the common error may be determined to include
one or more of an airflow error associated with an airflow path
delivering air to both the direct fuel injector and the port fuel
injector, and a fuel-type error associated with the fuel injected
by both the direct fuel injector and the port fuel injector. In
another example, the common error may be a common fuel type error
caused by changes in fuel quality resulting from changes in fuel
temperature, density, viscosity and chemical composition. In other
examples, the common error may be air error attributed to a
degraded air sensor (such as mass air flow sensor 120, pressure
sensor 122 and/or throttle position sensor 58 at FIG. 1). As such,
the controller may not be able to differentiate a common error
occurring due to a common fuel type error from a common error
occurring due to an air error. In one example, an engine may be
operating with both Kamrf.sub.DI and Kamrf.sub.PFI determined as
0.7 but a rich threshold level may be determined as 0.9. Since,
both slopes are equal and outside the threshold error level, a rich
common error of 0.3 (1.0-0.7) may be detected. After determining
the common error, method 300 proceeds to 332.
[0058] At 332, the routine updates a transfer function of the
direct and port fuel injectors to compensate for the common error
determined at 330 as follows:
Kamrf.sub.DI-new=Kamrf.sub.DI-old+common error (Eq. 7)
Kamrf.sub.PFI-new=Kamrf.sub.PFI-old+common error (Eq. 8)
As shown in the above example, Kamrf.sub.DI and Kamrf.sub.PFI will
change from 0.7 to 1.0 and the common error is taken as 0.3.
[0059] After determining one of the DI, PFI, and common error,
method 300 proceeds to 334 (from each of 320, 326, and 332). At
334, the method includes applying distinct mitigating actions based
on whether the system air-fuel error was due to a port injector
error, a direct injector error, or a common error. In addition,
distinct diagnostic codes may be set responsive to the indication
of a DI error (or degraded direct injector), a PFI error (or
degraded port injector), or a common error. For example, the
routine may limit fuel injection to direct and port fuel injectors
with lower fueling errors while disabling injectors with larger
fueling errors. For example the error associated with the direct
fuel injector may be compared to the error associated with the port
fuel injector; and based on the comparison, one of the direct and
port fuel injector having a larger error may be deactivated and the
engine may be fueled with a remaining one of the direct and port
fuel injector having a smaller error. As another example, if the
direct injection system is determined to be degraded at 318, then
responsive to the DI error, the controller may disable direct
injection and fuel the engine via port injection only. Likewise, if
the port injection system is determined to be degraded at 324, then
responsive to the PFI error, the controller may disable port
injection and fuel the engine via direct injection only. After
updating the transfer functions of direct and port fuel injectors,
the routine may exit.
[0060] Returning to 328, if the slope of the adapted fuel
multiplier values and fraction of directly injected fuel
(Kamrf.sub.DI) is not equal to the slope of the adapted fuel
multiplier values and fraction of port injected fuel
(Kamrf.sub.PFI), the routine proceeds to 336. At 336, the routine
determines DI and PFI errors based on Kamrf.sub.DI and
Kamrf.sub.PFI values less than the first and second threshold
slopes, respectively. Next at 338, method 300 identifies degraded
direct and port fuel injectors based on DI and PFI errors
determined at 336. Further, the routine updates a transfer function
of each degraded direct and port fuel injector to compensate for
the DI and PFI error. After, identifying the degraded fuel
injectors and updating the corresponding transfer functions, method
300 proceeds to 340. At 340, the routine operates fuel injectors
with the updated transfer functions to deliver fuel to the engine,
and subsequently the routine exits.
[0061] In this way, direct injector error may be identified based a
first slope determined as a ratio of a rate of change of an
air-fuel error and a fraction of fuel injected via direct
injection, and a port fuel injector error may be identified based
on a second slope determined as a ratio of a rate of change of an
air-fuel error and a fraction of fuel injected via port injection.
By comparing the first and second slope, the DI and PFI errors may
be separated from a common error to reduce chances of
over-compensating for engine air-fuel errors. Further, DI and PFI
errors may be addressed by adjusting transfer functions of direct
and port fuel injectors to reduce engine emissions and improve
engine efficiency.
[0062] FIG. 4 shows an exemplary graphical output 400 for
determining fuel injector error in an engine fueled with both
direct and port fuel injectors. Method 400 will be described herein
with reference to methods and systems depicted in FIGS. 1-3.
[0063] As illustrated, the first graph represents engine speed
versus time at plot 402. The vertical axis represents engine speed
and engine speed increases in the direction of the vertical axis.
The second graph represents engine load versus time at plot 404.
The vertical axis represents engine load and engine load increases
in the direction of the vertical axis. The third graph represents a
fraction of directly injected fuel versus time at plot 406. The
vertical axis represents a fraction of directly injected fuel and
the fuel fraction increases in the direction of the vertical axis.
The fourth graph represents a fraction of port injected fuel versus
time at plot 408. The vertical axis represents a fraction of port
injected fuel and the fuel fraction increases in the direction of
the vertical axis. The fifth graph represents engine air-fuel ratio
or lambda versus time at plot 410. The vertical axis represents
engine air-fuel ratio or lambda and air-fuel ratio or lambda
increases in the direction of the vertical axis.
[0064] The sixth graph represents an adapted fuel multiplier versus
time at plot 414. The vertical axis represents the adapted fuel
multiplier and the value of the adapted fuel multiplier increases
in the direction of the vertical axis. The seventh graph represents
a slope of fuel multiplier values and a fraction of fuel injected
via direct injection, and a slope of fuel multiplier values and a
fraction of fuel injected via port injection versus time. The
vertical axis represents the slope of fuel multiplier values and
the fraction of directly injected fuel, the slope of fuel
multiplier values and the fraction of port injected fuel, and both
slopes increase in the direction of the vertical axis. Line 418
represents the slope of fuel multiplier values and the fraction of
directly injected fuel and line 420 represents the slope of fuel
multiplier values and the fraction of port injected fuel. Line 422
represent a threshold level for a lean injector error and line 424
represents a threshold level for a rich injector error. The eighth
graph represents a slope of a common error versus time at plot 426.
The common error may be a common fuel type error or air measurement
error. The vertical axis represents the slope of the common error
and the slope increases in the direction of the vertical axis. Line
428 represents a threshold level for a lean common error and line
430 represents a threshold level for a rich common error.
[0065] The ninth graph represents a transfer function of a direct
injection system versus time at plot 432. The vertical axis
represents the transfer function of a direct injection system and
the transfer function increases in the direction of the vertical
axis. The tenth graph represents a transfer function of a port fuel
injection system versus time at plot 434. The vertical axis
represents the transfer function of a port fuel injection system
and the transfer function increases in the direction of the
vertical axis. For lines 432 and 434, a value of "1" represents
updating a transfer function of an engine injector and a value of
"0" represents not updating a transfer function of an engine
injector. The horizontal axes of each plot represent time and time
increases from the left side of the figure to the right side of the
figure.
[0066] Between T0 and T1, engine is operating at a lower engine
speed (402) and engine load (404), and as a result a fraction of
directly injected fuel (406) may be kept low and fraction of port
injected fuel (408) may be maintained at a high level. Larger
fractions of port injected fuel may be desirable at lower engine
speeds and loads since fuel injected via port fuel injection
quickly evaporates to reduce build-up of particulate matter and
improve engine emissions. On the other hand, smaller fractions of
directly injected fuel may be applied at low engine speeds and
loads to reduce soot formation and spark plug fouling. The engine
air-fuel ratio or lambda (410) measured at an exhaust gas sensor
(such as exhaust gas sensor 126 at FIG. 1) is oscillating about a
stoichiometric air-fuel ratio (412). The adapted fuel multiplier
(414) may oscillate about an initial fuel multiplier value (416)
corresponding to a condition with no engine air-fuel error. Since
the engine air-fuel ratio is close to the stoichiometric level and
the slopes of fuel multiplier values and fraction of injected fuel
(for both direct and port fuel injectors) and the slope of common
error do not exceed threshold values, the transfer functions of the
direct injectors (432) and port fuel injectors (434) may not be
updated.
[0067] At T1, the engine speed and load may increase in response to
an increase in driver demand torque, for example. The fraction of
directly injected fuel may increase while the fraction of the port
injected fuel may decrease. Applying large fractions of directly
injected fuel at higher engine speeds and loads may enhance
cylinder charge cooling to reduce the possibility of engine knock.
The engine air-fuel ratio may slightly decrease below the
stoichiometric air-fuel ratio and adapted fuel multiplier value may
slightly fall below the initial fuel multiplier value. The slopes
of fuel multiplier values and fraction of injected fuel for both
direct and port fuel injectors remain within threshold error
levels. Likewise, the slope of the common error remains below
threshold levels for the common error. Thus, adapting learning of
fuel multiplier values may continue and the transfer functions of
the direct and port fuel injectors may not be updated.
[0068] Between T1 and T2, the engine speed and load may continue to
increase in response to an increase in driver demand torque. The
fraction of directly injected fuel may continue to increase while
the fraction of the port injected fuel may continue to decrease.
The engine lambda continues to oscillate about the stoichiometric
air-fuel ratio and the adapted fuel multiplier oscillates about the
initial fuel multiplier value. The transfer functions of the direct
and port fuel injectors may not be updated since the adapting
learning has not reached a mature level. A learning maturity level
may be determined based a learning duration exceeding a threshold
duration. Alternatively, the maturity level may be determined based
on a difference between current and previous fuel multiplier values
exceeding a threshold fuel multiplier difference.
[0069] Prior to T2, the engine air-fuel ratio may increase above
the stoichiometric air-fuel ratio and the adapted fuel multiplier
may increase above the initial fuel multiplier value. Consequently,
the slope of the adapted fuel multiplier values and fraction of
directly injected fuel may increase and exceed the threshold level
for a lean injector error while the slope of the adapted fuel
multiplier values and a fraction of port injected fuel remains
below threshold error values. The slope of common error may remain
within threshold levels for the common error. Since the slope of
the adapted fuel multiplier values and fraction of directly
injected fuel exceeds the threshold level for the lean injector
error, it may be determined that one or more direct fuel injectors
may be degraded. An engine controller may be programed to store the
magnitude of fueling error and identity of the degraded direct fuel
injectors. The controller evaluates a change in the air fuel ratio
from a closed loop controller or a change in the adaptive fuel
multipliers and updates the DI slope (Kamrf.sub.DI) as disclosed
earlier at FIG. 3. Similarly, the controller evaluates a change in
the air fuel ratio from the closed loop controller or the change in
the adaptive fuel multipliers and updates the PFI slope
(Kamrf.sub.PFI) as disclosed earlier at FIG. 3. The controller may
be further adjusted to update the transfer functions of the direct
injectors during a subsequent engine operation. It may be further
determined that none of the port fuel injectors are degraded since
the slope of the adapted fuel multiplier values and fraction of
port injected fuel is within threshold levels. Likewise, it may be
determined that the common error is not present since the slope of
common error is within threshold values.
[0070] In one example, the slope of fuel multiplier values and
fraction of directly injected fuel may be determined as 1.3 but the
threshold level for a lean injector error is 1.1. Since, the
calculated DI slope correction factor is greater than the threshold
level for a lean injector error, it may be determined that one or
more direct fuel injectors may be degraded. Furthermore, the slope
of fuel multiplier values and fraction of port injected fuel may be
determined as 0.98 but a threshold level for a lean injector error
is 1.1 and a threshold level for a rich injector error is 0.9.
Since, the calculated PFI slope correction factor of 0.98 is within
both threshold levels it may be determined that none of the port
fuel injectors are degraded.
[0071] At T2, since one or more direct fuel injectors may be
degraded, the transfer function (432) of the direct injectors may
be updated by injecting a large fuel mass proportionate with the
magnitude of the fueling error. The transfer function (434) of the
port fuel injectors may not be updated since none of the port
injectors exhibits any fueling error. The direct fuel injectors
with large fueling error may be shut off and engine may be operated
with direct injectors with lower error and revised transfer
functions. Further, all port injectors may remain operational.
Subsequently, the engine speed and load may continue to increase
due to an increase in driver demand torque. The fraction of
directly injected fuel may increase gradually while the fraction of
port injected fuel may decrease slowly. The engine lambda may
decrease to the stoichiometric air-fuel ratio and the adapted fuel
multiplier may decrease to the initial fuel multiplier value. The
slope of the adapted fuel multiplier and fraction of directly
injected fuel may decrease to threshold levels while the slope of
the adapted fuel multiplier and fraction of port injected fuel may
remain within threshold levels. Likewise, the slope of the common
error may remain within threshold levels.
[0072] Between T2 and T3, direct fuel injectors with low fueling
error and updated transfer functions are operated to compensate for
the fueling error determined previously at T2. The updating of the
transfer functions of the direct fuel injectors may continue for a
short duration before stopping. In addition, all the port fuel
injectors remain operational. The engine speed and load may remain
steady for a while before decreasing. The fractions of directly
injected fuel maybe maintained at high levels while fractions of
port injected fuel maybe kept at low values. The engine lambda
continues to oscillate about the stoichiometric air-fuel ratio and
the adapted fuel multiplier oscillates about the initial fuel
multiplier value.
[0073] Prior to T3, the engine air-fuel ratio may decrease below
the stoichiometric air-fuel ratio and the adapted fuel multiplier
may decrease below the initial fuel multiplier value. But the slope
of the adapted fuel multiplier values and fraction of directly
injected fuel may remain within threshold levels. However, the
slope of the adapted fuel multiplier values and a fraction of port
injected fuel may drop below the threshold level for a rich
injector error. The slope of common error may remain within
threshold levels. Since the slope of the adapted fuel multiplier
values and fraction of directly injected fuel is within threshold
levels, it may be determined that none of the operating direct fuel
injectors are degraded. However, one or more port fuel injectors
may be degraded since the slope of the adapted fuel multiplier
values and fraction of port injected fuel is outside the threshold
level for a rich injector error. An engine controller may be
programed to store the magnitude of fueling error and identity of
the degraded port fuel injectors. The controller may be further
adjusted to update the transfer functions of the port injectors in
a subsequent engine operation. It may be further determined that no
common error is not present since the slope of the common error is
within threshold levels.
[0074] For example, the slope of fuel multiplier values and
fraction of directly injected fuel may be determined as 0.95 but a
threshold level for a lean injector error may be determined as 1.1
and a threshold level for a rich injector error may be 0.9. Since,
the calculated slope is within the threshold error levels, it may
be determined that none of the operating direct fuel injectors are
degraded. Furthermore, the slope of fuel multiplier values and
fraction of port injected fuel may be determined as 0.7 but the
threshold level for a rich injector error may be 0.9. Since, the
calculated slope of 0.7 is outside the threshold limit for the rich
injector error, it may be determined that one or more of the port
fuel injectors may be degraded, each degraded injector showing a
rich PFI error.
[0075] At T3, since none of the operating direct fuel injectors are
degraded, the transfer function of the direct injectors may not be
updated. However, the transfer function of the port fuel injectors
may be updated since one or more of the port injectors exhibit
fueling error. Updating the transfer function of the port fuel
injectors may include updating the amount of port injected fuel to
compensate for the fueling error. The port fuel injectors with
large fueling error may be shut off and engine may be operated with
port fuel injectors with updated transfer functions. Between T3 and
T4, port fuel injectors with low fueling error and updated transfer
functions are operated to compensate for the fueling error
determined previously. The updating of the transfer functions of
the port fuel injectors may continue for a short duration before
the updating process is stopped. In addition, all direct fuel
injectors with lower error remain operational. Subsequently, the
engine speed and load may decrease gradually due to a reduction in
driver demand torque. The fraction of directly injected fuel may
decrease gradually while the fraction of port injected fuel may
increase slowly. The engine lambda may increase to the
stoichiometric air-fuel ratio and the adapted fuel multiplier may
increase to the initial fuel multiplier value. The slope of the
adapted fuel multiplier and fraction of directly injected fuel may
remain within threshold levels. But the slope of the adapted fuel
multiplier and fraction of port injected fuel may increase to
threshold levels. Further, the slope of the common error may remain
within threshold levels.
[0076] Prior to T4, the engine air-fuel ratio may again decrease
below the stoichiometric air-fuel ratio and the adapted fuel
multiplier may decrease below the initial fuel multiplier value.
The slope of the adapted fuel multiplier values and fraction of
directly injected fuel may remain within threshold levels.
Similarly, the slope of the adapted fuel multiplier values and a
fraction of port injected fuel may remain within threshold levels.
However, the slope of the common error may exceed the threshold for
a rich common error and it may be determined that a rich common
error is present. The common error may be a common fuel type error
caused by changes in fuel quality, for example. Alternatively, the
common error may be an air measurement error caused by a degraded
sensor such as an air mass, pressure or throttle position sensor.
The engine controller may set a diagnostic code to indicate the
common error, the diagnostic code distinct from codes set
responsive to a DI error or a PFI error. The controller may be
further programed to update the transfer functions of the both
direct and port fuel injectors in a subsequent engine operation to
compensate for the common error.
[0077] At T4, the transfer functions of the direct and port fuel
injectors may be updated due to the presence of the common error.
Updating the transfer function of the direct and port fuel
injectors may include updating the amount of fuel injected via both
direct and port fuel injection to compensate for the common error.
For example, the transfer function of the direct fuel injector may
be adjusted in response to learning an air-fuel ratio error as an
error associated with the direct fuel injector; the transfer
function of the port fuel injector may be adjusted in response to
learning an air-fuel ratio error as an error associated with the
port fuel injector; and adjusting the transfer function of each of
the direct fuel injector and the port fuel injector responsive to
learning an air-fuel ratio error as a common error. In one example,
direct and port fuel injectors with large fueling error may be shut
off and engine may be operated with only fuel injectors with lower
error. Subsequently, the engine speed and load may decrease to low
values due to a further reduction in driver demand torque. The
fraction of directly injected fuel may decrease to low value while
the fraction of port injected fuel may increase to a high value.
The engine lambda may increase to the stoichiometric air-fuel ratio
and the adapted fuel multiplier may increase to the initial fuel
multiplier value. The slope of the adapted fuel multiplier and
fraction of injected fuel (for both direct and port fuel injectors)
may remain within threshold levels. Further, the slope of the
common error may increase and remain within threshold levels.
[0078] Between T4 and T5, direct and port fuel injectors with low
fueling error may be operated to compensate for the common error
determined prior to T4. The updating of the transfer functions of
the direct and port fuel injectors may continue for a short
duration before the updating process is stopped. The engine speed
and load are maintained at low values. The fractions of directly
injected fuel may remain at low values while fractions of port
injected fuel may stay at high values. The engine lambda continues
to oscillate about the stoichiometric air-fuel ratio and the
adapted fuel multiplier oscillates about the initial fuel
multiplier value.
[0079] In this way, direct injector error may be identified based
on a slope of an air-fuel error and a fraction of fuel injected via
direct injection, a port fuel injector error may be identified
based on a slope of an air-fuel error and a fraction of fuel
injected via port injection. By comparing the first and second
slope, direct and port fuel injector errors may be separated from a
common error to provide better estimates of engine air-fuel error.
Further, fueling errors of direct and port fuel injectors may be
addressed by adjusting DI and PFI transfer functions to reduce
engine emissions and improve engine efficiency.
[0080] Referring to FIG. 5, an example method 500 is shown for
determining fueling errors in an engine with direct and port fuel
injectors. The method enables the portion of an air-fuel ratio
error that is due to a common error to be differentiated from the
portions of the error that is due to a direct injector and a port
injector. Accordingly, direct and port injector transfer function
adjustments may be updated to account for the common error portion.
A fueling error of direct fuel injectors may be determined based on
a slope of adapted fuel multiplier values and a fraction of
directly injected fuel. Similarly, port injector error may be
determined based on a slope of adapted fuel multiplier values and a
fraction of port injected fuel. Further, a common error may be
separated from direct and port fuel injector error based on a
comparison of the DI and PFI slopes. In addition, fueling errors of
the direct and port fuel injectors may be adjusted based on the
common error. Instructions for carrying out method 500 and the rest
of the methods included herein may be executed by a controller
based on instructions stored on a memory of the controller and in
conjunction with signals received from sensors of the engine
system, such as the sensors and output described above with
reference to FIG. 1. The controller may employ engine actuators of
the engine system to adjust engine operation, according to the
methods described below.
[0081] At 502, method 500 operates an engine in closed loop
air-fuel control mode. During closed loop air-fuel control, a
controller (such as controller 12 at FIG. 1) determines a desired
engine air-fuel ratio by indexing tables and/or functions based on
driver demand torque, engine speed, and other conditions. Fuel may
be injected into the engine via direct and port fuel injectors to
provide the desired engine air-fuel ratio and feedback from an
exhaust gas sensor (such as exhaust gas sensor 126 at FIG. 1) may
be used to adjust the amount of fuel injected. A fraction of fuel
injected via direct and port fuel injectors may be determined based
on engine load and speed, such as by indexing a look-up table. As
an example, at lower engine speeds and loads, a larger portion of
the total fuel amount may be delivered via port injection. As
another example, at higher engine speeds and loads, a larger
portion of the total fuel amount may be delivered via direct
injection.
[0082] Next at 504, method 500 adapts a value of a fuel multiplier
based on sensor readings at the exhaust gas sensor. The exhaust gas
sensor may indicate a lean or rich fuel mixture depending on engine
operating conditions. Specifically, if the exhaust gas sensor
indicates a lean or rich air-fuel error over an extended duration,
an adapted fuel multiplier may be incremented or decremented from
an initial unit value to a new reading based on a magnitude of the
measured air-fuel error. The adapted fuel multiplier may be learned
at a plurality of engine speed and load conditions, as well as a
range of engine air masses/air mass flows and stored in a memory of
the controller. In addition, the fractions of direct and port
injected fuel corresponding to the adapted fuel multiplier and
engine speed-loads may be stored in the memory of the engine
controller. After learning and adjusting fuel multiplier values at
different engine loads and speeds, the routine proceeds to 506.
[0083] At 506, method 500 determines if the adaptive learning has
reached a mature learning limit. The learning limit may be based on
a number of times the adapted fuel multiplier values have been
updated. Alternatively, the learning limit may be reached during
the adapting learning if a difference between a current value and
previous value of a fuel multiplier exceeds a threshold difference.
Furthermore, the routine may determine if a sufficient number of
adapted fuel multiplier values (and corresponding direct and port
fuel fractions) have been stored in the memory of the engine
controller. If the adapting learning has reached the mature
learning limit, the routine proceeds to 508. Otherwise, if the
adapting has not matured, the routine proceeds to 510 to continue
monitoring air-fuel ratio errors and fuel fault conditions.
[0084] Next at 508, method 500 determines if any of the adapted
fuel multiplier values are out of range. If the answer is YES and
method 500 proceeds to 512. Otherwise, the answer is NO and no
further adjustments are performed to the adaptive fuel multipliers.
The routine then exits.
[0085] At 512, the routine determines a slope of an adapted fuel
multiplier and fraction of directly injected fuel at different
engine loads and speeds. An example slope is illustrated at FIG.
2B, where a slope of adapted fuel multiplier values and fraction of
directly injected fuel is determined for an engine operating with
speeds in a range of 500-5000 rpm and loads in a range of 0.4-0.8.
The slope of the adapted fuel multiplier values and fraction of
directly injected fuel may be determined as:
Kamrf DI = d ( Kamrf ) d ( F DI ) ( Eq . 9 ) ##EQU00004##
where Kamrf.sub.DI is a slope of the adapted fuel multiplier values
and fraction of the directly injected fuel, Kamrf is the adapted
fuel multiplier, F.sub.DI is the fraction of directly injected
fuel. After determining the slope of the adapted fuel multiplier
values and fraction of directly injected fuel, method 500 proceeds
to 514.
[0086] At 514, the routine determines a slope of an adapted fuel
multiplier and fraction of port injected fuel at different engine
loads and speeds. An example slope is illustrated at FIG. 2B, where
a slope of adapted fuel multiplier values and fraction of port
injected fuel is determined for an engine operating at speeds in a
range of 2000-5000 and loads in a range of 0.4-0.8. The slope of
the adapted fuel multiplier values and fraction of port injected
fuel may be determined as:
Kamrf PFI = d ( Kamrf ) d ( F PFI ) ( Eq . 10 ) ##EQU00005##
where Kamrf.sub.PFI is the slope of the adapted fuel multiplier
values and fraction of the port injected fuel and F.sub.PFI is the
fraction of port injected fuel. After determining the slope of the
adapted fuel multiplier values and fraction of port injected fuel,
method 500 proceeds to 516.
[0087] At 516, the routine determines if the absolute slope of the
adapted fuel multiplier values and fraction of directly injected
fuel (Kamrf.sub.DI) and the absolute slope of the adapted fuel
multiplier values and fraction of port injected fuel
(Kamrf.sub.PFI) is greater than a threshold slope. The threshold
slope may be based on a maximum rich or lean air-fuel ratio less
than an air-fuel ratio value based on fuel emissions standard.
Alternatively, it may be determined if an error correction
coefficient for each of the direct fuel injection and the port
injection is higher than the threshold. If the calculated slope is
greater than the threshold slope, the routine proceeds to 518.
Otherwise, the routine proceeds to 520.
[0088] Next at 518, method 500 determines fueling error of direct
and port fuel injectors and a common error. In this case, it may be
assumed that the total error has a first direct injection error
component, a second port injector error component, and a third
common error component. Therefore, it may be desirable to separate
the direct and the port fuel injector error from the common error
to enable appropriate correction of DI and PFI transfer functions.
For example, learning at least a portion of an air-fuel ratio error
as a common error may include learning a first portion of the
air-fuel ratio error as the common error and a second, remaining
portion of the air-fuel ratio error as an error associated with a
first port fuel injector and/or a second direct fuel injector,
wherein the first portion is based on a minimum of a first slope of
the PFI error and the second slope of the DI error, as elaborated
below. The first fuel injector may be a direct fuel injector and
the second fuel injector may be a port fuel injector.
[0089] In another example, degradation of a port fuel injector may
be indicated when a ratio of a change in air-fuel error to a change
in fuel fraction from the port fuel injector is higher than a
threshold; degradation of a direct fuel injector may be indicated
when a ratio of a change in air-fuel error to a change in fuel
fraction from the direct fuel injector is lower than a threshold;
an engine fueling error due to the common error may be indicated
when the ratio of the change in air-fuel error to the change in
fuel fraction from each of the port and the direct injector is
higher than the threshold and the ratio of the change in air-fuel
error to the change in fuel fraction from the port injector is
within a threshold of the ratio of the change in air-fuel error to
the change in fuel fraction from each of the direct injector. The
air-fuel error may be determined based on a difference between a
commanded air-fuel ratio and an actual air-fuel ratio estimated by
the air-fuel ratio sensor, and wherein the change in air-fuel ratio
error is learned as a change in an adapted fuel multiplier
commanded to each of the port and the direct fuel injector.
[0090] The common error, Kamrf.sub.CE is determined based on a
minimum value of a difference between a unit value and a calculated
slope of each individual direct and port fuel injector as shown by
the equation below.
Kamrf.sub.CE=min{(1-Kamrf.sub.DI),(1-Kamrf.sub.PFI)} (Eq. 11)
A correction for a fueling error in an engine may be made by
adjusting fractions of fuel delivered via direct and port fuel
injection as shown by the equation below.
Kamrf.sub.corr=Kamrf.sub.DI(F.sub.DI)+Kamrf.sub.PFI(F.sub.PFI) (Eq.
12)
where, Kamrf.sub.curr is a fuel correction to compensate for DI and
PFI error in an engine. However, if a common error is grouped
together with fueling error of both direct and port fuel injectors,
then the fuel correction shown in Eq. 8 may overcompensate for DI
and PFI errors. Therefore, it is desirable to separate the common
error from fueling error of direct and port fuel injectors prior to
correcting for engine air-fuel error. For example, an engine may be
fueled by injecting fuel to a cylinder via a first fuel injector
and a second fuel injector; and an error associated with the first
fuel injector or the second fuel injector is distinguished from a
common fuel system error as a function of a rate of change of
air-fuel ratio error and a fraction of fuel injected via the first
fuel injector or the second fuel injector, as elaborated with
reference to FIG. 6. Further, injecting fuel into the cylinder may
be performed in each of a plurality of engine air mass flow regions
and wherein the error associated with the first fuel injector or
the second fuel injector and the common fuel system error is
learned in each of the plurality of engine air mass flow regions as
a function of air mass flow.
[0091] In other examples, fuel may be injected into an engine
cylinder via a first fuel injector and a second fuel injector
during a cylinder cycle, the first and second fuel injector having
distinct types of fuel injection; and then selectively assigning an
air-fuel error from the cylinder during the cylinder cycle to a
common error associated with the fuel system based on each of a
first fuel fraction provided by the first fuel injector, a second
fuel fraction provided by the second fuel injector, and the
air-fuel error. In one example, the selective assigning of the
air-fuel error from the cylinder may further include learning a
first rate of change in the air-fuel error with a change in the
first fuel fraction; learning a second rate of change in the
air-fuel error with a change in the second fuel fraction; and if
the first rate is within a threshold difference of the second rate,
and each of the first and second rate are higher than a threshold,
assigning the air-fuel error to the common error. In another
example, the selective assigning of the air-fuel error from the
cylinder may further include assigning a first portion of the
air-fuel error to the first fuel injector if the first rate is
outside the threshold difference of the second rate while the first
and the second are higher than the threshold, the first portion
based on the first fuel fraction provided by the first fuel
injector; and assigning a second portion of the air-fuel error to
the second fuel injector, the second portion based on the second
fuel fraction provided by the second fuel injector. In other
examples, the selective assigning of the air-fuel error may further
include assigning an adapted fuel multiplier corresponding to the
common error to each of the first and the second fuel injector;
wherein the adapted fuel multiplier corresponding to the common
error is a first multiplier that is distinct from a second
multiplier corresponding to the first portion of the air-fuel error
that is assigned to only the first fuel injector, and is also
distinct from a third multiplier corresponding to the second
portion of the air-fuel error that is assigned to only the second
fuel injector.
[0092] Next at 522, method 500, may update the slope of adapted
fuel multipliers and a fraction of directly injected fuel to
account for a portion of the common error grouped together with the
direct injector error. Similarly, the slope of adapted fuel
multipliers and fraction of port injected fuel may be updated to
account for a portion of the common error that may be grouped
together with the port fuel injector error. An updated slope of the
adapted fuel multipliers and a fraction of fuel injected via direct
injector (Kamrf.sub.DI.sub._.sub.new) and an updated slope of the
adapted fuel multipliers and a fraction of fuel injected via port
fuel injector (Kamrf.sub.PFI.sub._.sub.new) may be determined at
each cell of the adaptive fuel multiplier table by subtracting the
common error from values of kamrf.sub.DI determined at 512 (renamed
hereafter as Kamrf.sub.DI.sub._.sub.old) and Kamrf.sub.PFI
determined at 514 (renamed hereafter as
Kamrf.sub.PFI.sub._.sub.old), as show in equations below.
Kamrf.sub.DI.sub._.sub.new=Kamrf.sub.DI.sub._.sub.old-Kamrf.sub.CE
(Eq. 13)
Kamrf.sub.PFI.sub._.sub.new=Kamrf.sub.PFI.sub._.sub.old-Kamrf.sub.CE
(Eq. 14)
[0093] For example, a slope of adapted fuel multiplier values and a
fraction of directly injected fuel (kamrf.sub.DI) may be determined
as 1.6. Similarly, a slope of adapted fuel multiplier values and a
fraction of port injected fuel (kamrf.sub.PFI) may be determined as
1.3. A common error of 0.3 may be determined based on the DI and
PFI slopes. By subtracting the common error of 0.3 from the
individual direct and port fuel injector errors, an updated DI
slope of 1.3 (1.6-0.3) and updated PFI slope of 1.0 (1.3-0.3) may
be determined. Further, a threshold slope may be determined as 0.6,
and threshold levels for a rich and a lean injector error may be
determined as 0.9 and 1.1, respectively. The updated DI slope is
determined to be greater than the threshold slope and the threshold
level for a lean injector error. Therefore, it may be determined
that a lean direct fuel injector error may be present. The PFI
slope is determined to be greater than the threshold slope but
within the threshold levels for the rich and lean injector error.
Therefore, it may be determined that none of the port fuel
injectors are degraded. In this way, direct and port fuel injector
errors may be separated from the common error to minimize
overcompensating for fueling errors while improving engine
emissions.
[0094] Next at 524, the routine updates the common error in each
cell of the adaptive fuel multiplier table based on a portion of
the common error grouped together with the direct and port fuel
injector errors. The routine determines a corrected common error
(Tcorr.sub.new) at each cell of the adaptive fuel multiplier table
by adding the common error (Kamrf.sub.CE) determined at 518 to a
portion of a common error that may be grouped together with the
fueling error of both direct and port fuel injectors (Tcorr) as
shown in the equation below. The corrected common error is then
stored in each cell of the adapted fuel multiplier table. The
common error is directly added to the adaptive multiplier table
disclosed in FIG. 2A.
Tcorr.sub.new=Tcorr+Kamrf.sub.CE (Eq. 15)
[0095] At 526, the routine operates engine with direct and port
fuel injectors with lower fueling error. In this case, both direct
and port fuel injectors with large fueling error may be disabled.
In one example, a first fuel injector or a second fuel injector may
be operated in response to a greater of a first portion and a
second portion of an air-fuel error. In another example, fuel
injected into an engine may be adjusted to update an adapted fuel
multiplier commanded to a direct fuel injector while disabling a
port injector responsive to degradation of the port fuel injector;
and an adapted fuel multiplier commanded to a port fuel injector
may be updated while disabling a direct injector responsive to
degradation of the direct fuel injector. The routine proceeds to
exit after adjusting engine to operate with direct and port fuel
injectors with lower error.
[0096] Returning to 516, if the routine determines that the slope
of adapted fuel multipliers and fraction of directly injected fuel
is not greater than the first threshold slope, method 500 proceeds
520. At 520, method 500 determines that there is no common error.
Further, fueling error of direct and port fuel injectors may be
determined based on absolute values of Kamrf.sub.DI and
Kamrf.sub.PFI less than the first threshold. In this case, the DI
and PFI errors may be smaller than fuel injector errors determined
earlier at 518. Next at 528, degradation of direct and port fuel
injector may be indicated based on direct and port fuel injector
errors. For example, a slope of adapted fuel multiplier values and
a fraction of directly injected fuel may be determined as 0.75.
Similarly, a slope of adapted fuel multiplier values and a fraction
of port injected fuel may be determined as 0.98. Further, a
threshold slope may be determined as 0.8, and a threshold level for
a rich and lean injector error may be determined as 0.9 and 1.1,
respectively. The DI slope is determined to be less than the
threshold slope and the outside the threshold level for the rich
injector error. Therefore, it may be determined that a rich DI
error may be present. The PFI slope is determined to be greater
than the threshold slope and within the threshold levels for
injector error. Therefore, it may be determined that none of the
port fuel injectors are degraded.
[0097] At 530, the routine updates transfer functions of direct and
port fuel injectors indicating degradation. The updating may
include injecting a predetermined fuel amount into engine to
compensate for any fuel injector error determined at 520. For
example, if a lean DI error is indicated, an engine controller may
be adjusted to inject more fuel into the engine to compensate for
the DI error. Alternatively, the engine controller may be adjusted
to inject less air into engine to compensate for the DI error. Next
at 532, method 500 operates fuel injectors with updated transfer
functions and proceeds to exit.
[0098] In this way, fueling error of direct and port fuel injectors
delivering fuel to an engine may be determined based on a ratio of
a rate of change of fuel multiplier values and fractions of
injected fuel at different engine operating conditions. One or more
direct fuel injectors may be degraded if the slope of the fuel
multiplier values and fraction of directly injected fuel exceeds a
first threshold slope. Likewise, one or more port fuel injectors
may be degraded if the slope of fuel multiplier values and fraction
of port injected fuel exceeds a second threshold slope. By
comparing the ratio of the rate of change of air-fuel error and
fuel fraction of the direct and port fuel injection systems, a
common fuel type or air measurement error may be determined. In
this way, it may be possible to distinguish between fueling errors
of direct and port fuel injection systems from common error.
[0099] Referring to FIG. 6, an exemplary graphical output 600 is
shown for determining fuel injector error and common error in an
engine fueled via both direct and port fuel injectors. Method 600
will be described herein with reference to methods and systems
depicted in FIGS. 1-2, and FIG. 5.
[0100] As illustrated, the first graph represents engine speed
versus time at plot 602. The vertical axis represents engine speed
and engine speed increases in the direction of the vertical axis.
The second graph represents engine load versus time at plot 604.
The vertical axis represents engine load and engine load increases
in the direction of the vertical axis. The third graph represents a
fraction of directly injected fuel versus time at plot 606. The
vertical axis represents a fraction of directly injected fuel and
the fuel fraction increases in the direction of the vertical axis.
The fourth graph represents a fraction of port injected fuel versus
time at plot 608. The vertical axis represents a fraction of port
injected fuel and the fuel fraction increases in the direction of
the vertical axis. The fifth graph represents engine air-fuel ratio
or lambda versus time at plot 610. The vertical axis represents
engine air-fuel ratio or lambda and air-fuel ratio or lambda
increases in the direction of the vertical axis.
[0101] The sixth graph represents an adapted fuel multiplier versus
time at plot 614. The vertical axis represents the adapted fuel
multiplier and the value of the adapted fuel multiplier increases
in the direction of the vertical axis. The seventh graph represents
a slope of fuel multiplier values and a fraction of directly
injected fuel (kamrf.sub.DI) versus time at plot 618. The vertical
axis represents the slope of fuel multiplier values and the
fraction of directly injected fuel and the slope increases in the
direction of the vertical axis. Line 622 represents a lean
threshold level for the direct fuel injector and line 624
represents a rich error threshold level for the direct fuel
injector. The eighth graph represents a slope of fuel multiplier
values and a fraction of port injected fuel (kamrf.sub.PFI) versus
time at plot 626. The vertical axis represents the slope of fuel
multiplier values and the fraction of port injected fuel and the
slope increases in the direction of the vertical axis. Line 630
represents a lean threshold level for the port fuel injector and
line 632 represents a rich threshold level for the port fuel
injector.
[0102] The ninth graph represents a slope of a common error versus
(kamrf.sub.CE) time at plot 634. The common error may be a common
fuel type error or air measurement error. The vertical axis
represents the slope of the common error and the slope increases in
the direction of the vertical axis. Line 638 represents a lean
threshold level and line 640 represents a rich threshold level of
the common error.
[0103] The tenth graph represents a transfer function of a direct
injection system versus time at plot 642. The vertical axis
represents the transfer function of a direct injection system and
the transfer function increases in the direction of the vertical
axis. The eleventh graph represents a transfer function of a port
fuel injection system versus time at plot 644. The vertical axis
represents the transfer function of a port fuel injection system
and the transfer function increases in the direction of the
vertical axis. For lines 632 and 644, a value of "1" represents
updating a transfer function of an engine injector and a value of
"0" represents not updating a transfer function of an engine
injector. The horizontal axes of each plot represent time and time
increases from the left side of the figure to the right side of the
figure.
[0104] Between T0 and T1, engine is operating at a lower engine
speed (602) and engine load (604), and as a result a fraction of
directly injected fuel (606) may be kept low and fraction of port
injected fuel (608) may be maintained at a high level. Larger
fractions of port injected fuel may be desirable at lower engine
speeds and loads since fuel injected via port fuel injector quickly
evaporates to reduce buildup of particulate matter and improve
engine emissions. On the other hand, small fractions of directly
injected fuel are applied at low engine speeds and loads to reduce
soot formation and spark plug fouling. The engine air-fuel ratio or
lambda (610) measured at an exhaust gas sensor (such as exhaust gas
sensor 126 at FIG. 1) is oscillating about a stoichiometric
air-fuel ratio (612). The adapted fuel multiplier (614) may
oscillate about an initial fuel multiplier value (616)
corresponding to a condition with no engine air-fuel error. Since
the engine air-fuel ratio is close to stoichiometric and the slope
of fuel multiplier values and fraction of fuel injected (via both
direct and port fuel injectors) and the slope of a common error is
within threshold levels for common error, the transfer functions of
the direct injectors (642) and port fuel injectors (644) may not be
updated.
[0105] At T1, the engine speed and load may increase in response to
an increase in driver demand torque, for example. The fraction of
directly injected fuel may increase while the fraction of the port
injected fuel may decrease. Applying large fractions of directly
injected fuel at higher engine speeds and loads may enhance
cylinder charge cooling to reduce the possibility of engine knock.
The engine air-fuel ratio may slightly decrease below the
stoichiometric level and the adapted fuel multiplier may slightly
fall below the initial fuel multiplier value. The slopes of fuel
multiplier values and fraction of fuel injected via both direct and
port fuel injectors (kamrf.sub.DI and kamrf.sub.PFI) may remain
below threshold levels. Likewise, the common error (kamrf.sub.CE)
may remain below threshold levels. The adapting learning of fuel
multiplier values may continue and the transfer functions of the
direct and port fuel injectors may not be updated.
[0106] Between T1 and T2, the engine speed and load may continue to
increase in response to an increase in driver demand torque. The
fraction of directly injected fuel may continue to increase while
the fraction of the port injected fuel may continue to decrease.
The engine air-fuel ratio continues to oscillate about the
stoichiometric level and the adapted fuel multiplier oscillates
about the initial fuel multiplier value. The transfer functions of
the direct and port fuel injectors may not be updated since the
adapting learning has not reached a mature level. A learning
maturity level may be determined based on a learning duration
exceeding a threshold duration. Alternatively, the learning
maturity level may be determined based on a difference between
current and previous fuel multiplier values exceeding a threshold
fuel multiplier difference.
[0107] Prior to T2, the engine air-fuel ratio may increase above
the stoichiometric level and the adapted fuel multiplier may
increase above the initial fuel multiplier value. Consequently, the
direct and port injected fuel errors (kamrf.sub.DI and
kamrf.sub.PFI) may increase and exceed the lean error threshold
level. Similarly, the common error (kamrf.sub.CE) may also increase
and exceed the lean common error threshold level. Since the direct
and port fuel injector errors exceed threshold error levels, it may
be determined that one or more direct and port fuel injectors may
be degraded. In addition to presence of both direct and port fuel
injector errors, it may also be determined that a common error is
present. However, the DI and PFI errors determined, may include a
portion of the common error. Therefore, there may be need to
separate the common error from the DI and PFI errors determined
prior to T2. In this case, a portion of the common error lumped
together with the DI error (618) is separated out and an updated DI
error may be determined as shown by dotted curve 620. Further, a
portion of the common error lumped together with the PFI error
(626) is separated out and an updated PFI error may be determined
as shown by dotted curve 628. Similarly, the portion of the common
error separated from the DI error (618) and PFI error (626) may be
added to the original common error (634) to determine an updated
common error (636).
[0108] For example, learning at least a portion of an air-fuel
ratio error as a common error may include learning a first portion
of the air-fuel ratio error as the common error and a second,
remaining portion of the air-fuel ratio error as an error
associated with the direct or the port fuel injector, wherein the
first portion is based on a minimum of the first slope and the
second slope. In another example, an engine may be fueled by
injecting fuel to a cylinder via a direct fuel injector and a port
fuel injector; and an error associated with the direct fuel
injector or the port fuel injector is distinguished from a common
fuel system error as a function of a rate of change of air-fuel
ratio error and a fraction of fuel injected via the direct fuel
injector or the port fuel injector. Further, injecting fuel into
the cylinder may be performed in each of a plurality of engine air
mass flow regions and wherein the error associated with the direct
fuel injector or the port fuel injector and the common fuel system
error is learned in each of the plurality of engine air mass flow
regions as a function of air mass flow.
[0109] In other examples, fuel may be injected into an engine
cylinder via a direct fuel injector and a port fuel injector during
a cylinder cycle, the direct and port fuel injector having distinct
types of fuel injection; and then selectively assigning an air-fuel
error from the cylinder during the cylinder cycle to a common error
associated with the fuel system based on each of a first fuel
fraction provided by the direct fuel injector, a second fuel
fraction provided by the port fuel injector, and the air-fuel
error. In one example, the selective assigning of the air-fuel
error from the cylinder may further include learning a first rate
of change in the air-fuel error with a change in the first fuel
fraction; learning a second rate of change in the air-fuel error
with a change in the second fuel fraction; and if the first rate is
within a threshold difference of the second rate, and each of the
first and second rate are higher than a threshold, assigning the
air-fuel error to the common error. In another example, the
selective assigning of the air-fuel error from the cylinder may
further include assigning a first portion of the air-fuel error to
the direct fuel injector if the first rate is outside the threshold
difference of the second rate while the first and the second are
higher than the threshold, the first portion based on the first
fuel fraction provided by the direct fuel injector; and assigning a
second portion of the air-fuel error to the port fuel injector, the
second portion based on the second fuel fraction provided by the
port fuel injector. In yet another example, an engine may be
operating with DI and PFI slopes of 1.6 and 1.3, respectively, and
a common error of 0.3. By subtracting the common error of 0.3 from
the individual direct and port fuel injector errors, an updated DI
slope of 1.3 (1.6-0.3) and an updated PFI slope of 1.0 (1.3-0.3)
may be determined. In this way, direct and port fuel injector
errors may be separated from the common error to minimize
overcompensating for fueling errors in a dual fuel engine while
improving engine emissions.
[0110] After separating the direct and port fuel injection errors
from the common error, an engine controller may be programed to
store the magnitude of DI and PFI errors, and common error. The
controller may also be programed to identify degraded direct and
port fuel injectors. The controller may set a diagnostic code to
alert a service technician about the common error.
[0111] For example, an operating engine may show an updated slope
of fuel multiplier values and a fraction of directly injected fuel
of 1.3 but a threshold level for a lean injector error is
determined as 1.1. Also, an updated slope of fuel multiplier values
and a fraction of port injected fuel may be determined as 1.2.
Further, a lean common error may be determined as 0.2 but a
threshold level for a lean common error may be determined as 0.15.
Since, the direct and port fuel injector errors exceed the
threshold level for injector error, it may be determined that one
or more direct and port fuel injectors may be degraded.
Furthermore, the common error is determined to be larger than the
threshold level of the lean common error. Thus, presence of a
common error may be confirmed. Consequently, an engine controller
may be adjusted (during a subsequent engine operation) to update
transfer functions of the direct and port fuel injectors to
compensate for DI and PFI errors, and common error.
[0112] At T2, since one or more direct and port fuel injectors may
be degraded, the transfer function of the direct injectors (642)
and port fuel injectors (644) may be updated. For example, the
update the transfer functions of the direct and port fuel injectors
may include injecting a large fuel mass (via direct and port fuel
injection) proportionate with the magnitude of the DI and PFI
error. The direct and port fuel injectors with large fueling error
may be shut off and engine may be operated with only direct and
port fuel injectors with lower error and updated transfer
functions.
[0113] In one example, fuel injected into engine may be adjusted to
update an adapted fuel multiplier commanded to a direct fuel
injector while disabling a port injector responsive to degradation
of the port fuel injector; and an adapted fuel multiplier commanded
to a port fuel injector may be updated while disabling a direct
injector responsive to degradation of the direct fuel injector.
[0114] The engine speed and load may continue to increase due to an
increase in driver demand torque. The fraction of directly injected
fuel may increase gradually while the fraction of port injected
fuel may decrease slowly. The engine air-fuel ratio may decrease to
the stoichiometric level, and the adapted fuel multiplier may
decrease to the initial fuel multiplier value. The slopes of the
adapted fuel multiplier and fraction of fuel injected via both DI
and PFI may decrease to threshold levels. Similarly, the common
error may decrease to threshold levels.
[0115] Between T2 and T3, direct and port fuel injectors with low
fuel injector error and updated transfer functions are operated to
compensate for the fuel injector error determined prior to T2. The
updating of the transfer functions of the direct fuel injectors may
continue for a short duration before the updating process is
stopped. The engine speed and load may remain steady for a while
before decreasing. The fractions of directly injected fuel maybe
maintained at high levels while fractions of port injected fuel
maybe kept at low values. The engine air-fuel ratio continues to
oscillate about the stoichiometric level, and the adapted fuel
multiplier may continue to oscillate about the initial fuel
multiplier value.
[0116] Prior to T3, the engine air-fuel ratio may decrease below
the stoichiometric air-fuel ratio and the adapted fuel multiplier
values may decrease below the initial fuel multiplier value. The
slope of the adapted fuel multiplier values and fraction of
directly injected fuel (618) may remain within threshold levels,
and thus it may be determined that there is no DI error. However,
the slope of the adapted fuel multiplier values and a fraction of
port injected fuel (626) may exceed the threshold level for a rich
injector error (632). The slope of common error may remain within
threshold levels, and it may be determined that no common error is
not present. It may be determined that one or more port fuel
injectors may be degraded since the slope of the adapted fuel
multiplier values and fraction of port injected fuel exceeds the
threshold level for rich injector error. An engine controller may
be programed to store the magnitude of PFI error and identity of
the degraded port fuel injectors.
[0117] For example, a slope of fuel multiplier values and a
fraction of directly injected fuel may be determined as 0.95 but a
threshold level for a rich injector error is determined as 0.9.
Since, the calculated DI slope is within the threshold level for
rich injector error, it may be determined that none of the
operating direct fuel injectors are degraded. Furthermore, the
slope of fuel multiplier values and fraction of port injected fuel
may be determined as 0.75 but a threshold level for a lean injector
error is determined as 1.1. Since, the PFI slope of 0.75 is outside
the threshold error levels of 0.9 and 1.1, it may be determined
that one or more of the port fuel injectors may be degraded with a
rich PFI error.
[0118] At T3, the transfer function of the port fuel injectors may
be updated since one or more of the port injectors exhibit fueling
error. Updating the transfer function of the port fuel injectors
may include updating the amount of port injected fuel to compensate
for the fueling error. For example, less fuel may be injected into
engine cylinders to compensate for the rich PFI error determined
prior to T3. Alternatively, more air may be injected into engine
cylinders to compensate for the port fuel injector error. Port fuel
injectors with large fueling error may be shut off and the engine
may be operated with port fuel injectors with updated transfer
functions and direct injectors with lower fueling error. Between T3
and T4, port fuel injectors with updated transfer functions may be
operated to compensate for the PFI error. The updating of the
transfer functions of the port fuel injectors may continue for a
short duration before the updating process is stopped. Further, all
direct fuel injectors with lower fueling error may remain
operational. Subsequently, the engine speed and load may decrease
gradually due to a reduction in driver demand torque. The fraction
of directly injected fuel may decrease gradually while the fraction
of port injected fuel may increase slowly. The engine air-fuel
ratio may increase to the stoichiometric level, and the adapted
fuel multiplier may increase to the initial fuel multiplier value.
The slope of the adapted fuel multiplier and fraction of directly
injected fuel may remain within threshold levels. The slope of the
adapted fuel multiplier and fraction of port injected fuel may
increase and remain within threshold levels. Further, the slope of
the common error may remain within threshold levels.
[0119] Prior to T4, the engine air-fuel ratio may again decrease
below the stoichiometric air-fuel ratio and the adapted fuel
multiplier may also decrease below the initial fuel multiplier
value. The slope of the adapted fuel multiplier values and fraction
of directly injected fuel may decrease and exceed the threshold
level for a rich injector error. Therefore, it may be determined
that a rich DI error may be present. The engine controller may be
programed to identify degraded direct fuel injectors and magnitude
of DI error. The controller may be further programed to update the
transfer functions of the both direct fuel injectors in a
subsequent engine operation to compensate for the DI error.
However, the slope of the adapted fuel multiplier values and a
fraction of port injected fuel may remain within threshold levels.
Likewise, the slope of the common error may remain with threshold
levels. It may be determined that there is no PFI error and common
error, and thus the transfer function of the port fuel injectors
may not be updated.
[0120] At T4, the transfer functions of the direct fuel injectors
(identified as degraded prior to T4) may be updated to compensate
for DI error. Updating the transfer function of the direct fuel
injectors may include updating the amount of fuel injected via
direct injection to compensate for the DI error. The direct fuel
injectors with large fueling error may be shut off and engine may
be operated with only fuel injectors with lower error.
Subsequently, the engine speed and load may decrease to low values
due to a further reduction in driver demand torque. The fraction of
directly injected fuel may decrease to low value while the fraction
of port injected fuel may increase to a high value. The engine
air-fuel ratio may increase to the stoichiometric level, and the
adapted fuel multiplier may increase to the initial fuel multiplier
value. The slope of the adapted fuel multiplier and fraction of
fuel injected via direct fuel injectors may increase and remain
within threshold levels. The slope of the adapted fuel multiplier
and fraction of port injected fuel may remain within threshold
levels. Further, the slope of the common error may remain within
threshold levels.
[0121] Between T4 and T5, direct fuel injectors with low fueling
error are operated with updated transfer functions to compensate
for the DI error determined prior to T4. The updating of the
transfer functions of the direct fuel injectors may continue for a
short duration before the updating process is stopped. The engine
speed and load are maintained at low values. The fractions of
directly injected fuel may remain at low values while fractions of
port injected fuel may stay at high values. The engine lambda
continues to oscillate about the stoichiometric air-fuel ratio and
the adapted fuel multiplier may oscillate about the initial fuel
multiplier value.
[0122] In this way, by binning air-fuel error correction
coefficients for individual injection systems over a range of air
mass cells, as engine speed-load conditions change, common
movements in the error of individual injection systems may be
better correlated with common errors. As such, this enables
individual injection system errors associated with a port or a
direct fuel injection system to be better distinguished from common
fuel or air errors, allowing for appropriate mitigating actions to
be taken. In particular, transfer functions for direct and port
injectors may be adjusted based on their individual errors while
accounting for common errors. In doing so, inaccurate disabling of
not degraded fuel injectors can be reduced. By more reliably
compensating adaptive multipliers responsive to air-fuel errors,
engine emissions may be improved.
[0123] In one example, a method comprises: fueling a cylinder via a
first and a second fuel injector; estimating each of a first
injection error of the first injector, a second injection error of
the second injector, and a common error as a function of an
air-fuel ratio error and a fraction of fuel injected via each of
the first and second injector; and correcting each of the first and
second error based on the common error. In the preceding example,
additionally or optionally, the common error is a fuel system error
common to each of the first and second injector, the common error
including one or more of an airflow error associated with an
airflow path delivering air to both the first fuel injector and the
second fuel injector, and a fuel-type error associated with the
fuel injected by both the first fuel injector and the second fuel
injector.
[0124] In any or all of the preceding examples, additionally or
optionally, estimating as a function of the air-fuel ratio error
and the fraction includes: dividing a rate of change of air-fuel
ratio error by the fraction of fuel injected via the first fuel
injector to determine a first slope; dividing the rate of change of
air-fuel ratio error by the fraction of fuel injected via the
second fuel injector to determine a second slope; and if the first
slope is within a threshold difference of the second slope, and
each of the first and second slope is higher than a threshold
value, learning a minimum of the first and second slope as the
common error. In any or all of the preceding examples, additionally
or optionally, correcting each of the first and second error based
on the common error includes: determining a correction factor based
on the common error; and reducing each of the first and the second
error by applying the correction factor. Any or all of the
preceding examples, may additionally or optionally further
comprise, adjusting a transfer function of the first fuel injector
with the reduced first error; adjusting a transfer function of the
second fuel injector with the reduced second error; and adjusting
fueling of the cylinder using the adjusted transfer function of the
first and the second fuel injector.
[0125] In any or all of the preceding examples, additionally or
optionally, the estimating further includes: if the first slope is
not within the threshold difference of the second slope, learning
the air-fuel ratio error as the error associated with the first
fuel injector when the first slope is higher than the threshold
value; and learning the air-fuel ratio error as the error
associated with the second fuel injector when the second slope is
higher than the threshold value. Furthermore, any or all of the
preceding examples, may additionally or optionally further
comprise, comparing the reduced first error with the reduced second
error; deactivating the first injector when the first error is
larger and fueling the engine with the second fuel injector; and
deactivating the second injector when the second error is larger
and fueling the engine with the first fuel injector. In any or all
of the preceding examples, additionally or optionally, the
injecting is performed in each of a plurality of engine air mass
flow regions and wherein each of the first, second, and common
error are learned in each of the plurality of engine air mass flow
regions as a function of air mass flow. In any or all of the
preceding examples, additionally or optionally, the first fuel
injector is a direct fuel injector and where the second fuel
injector is a port fuel injector.
[0126] In another example, a method for an engine fuel system, may
comprise: injecting fuel to an engine cylinder via a first fuel
injector and a second fuel injector during a cylinder cycle, the
first and second fuel injector having distinct types of fuel
injection; assigning a first portion of an air-fuel error from the
cylinder during the cylinder cycle to a first error associated with
the first fuel injector; assigning a second portion of the air-fuel
error to a second error associated with the second fuel injector;
and assigning a third portion of the air-fuel error to a common
error associated with the fuel system, wherein each of the first,
second, and third portion is based on each of a first fuel fraction
provided by the first fuel injector, a second fuel fraction
provided by the second fuel injector, and the air-fuel error. The
preceding example may additionally or optionally comprise, the
assigning includes: learning a first rate of change in the air-fuel
error with a change in the first fuel fraction; learning a second
rate of change in the air-fuel error with a change in the second
fuel fraction; and if the first rate is within a threshold
difference of the second rate, and each of the first and second
rate are higher than a threshold, assigning a minimum of the first
rate and the second rate to the common error. In any or all of the
preceding examples, additionally or optionally, the assigning
further includes: if the first rate is outside the threshold
difference of the second rate while the first and the second are
higher than the threshold, assigning the first portion based on the
first fuel fraction provided by the first fuel injector; and
assigning the second portion based on the second fuel fraction
provided by the second fuel injector.
[0127] Furthermore, any or all of the preceding examples, may
additionally or optionally further comprise, assigning a first
adaptive fuel multiplier corresponding to the first error to the
first fuel injector; assigning a second adaptive fuel multiplier
corresponding to the second error to the second fuel injector;
updating each of the first and second adaptive fuel multiplier with
a correction factor based on the common error; and adjusting
fueling of the engine with each of the updated first and second
adaptive fuel multipliers. Any or all of the preceding examples,
may additionally or optionally further comprise, limiting operation
of the first fuel injector in response to the first portion of the
air-fuel error being greater than the second portion; and limiting
operation of the second fuel injector in response to the second
portion of the air-fuel error being greater than the first portion.
In any or all of the preceding examples, additionally or
optionally, limiting operation of the first fuel injector includes
fueling the engine via only the second injector and wherein
limiting operation of the second fuel injector includes fueling the
engine via only the first injector.
[0128] In any or all of the preceding examples, additionally or
optionally, each of the first, second, and third portion are
learned as a function of air mass flow. Another example engine
system comprises: an engine including a cylinder; a port fuel
injector in fluidic communication with the cylinder; a direct fuel
injector in fluidic communication with the cylinder; an exhaust
air-fuel ratio sensor; and a controller including executable
instructions stored in non-transitory memory for: while operating
the engine with closed loop air-fuel ratio control based on
feedback from the air-fuel ratio sensor, updating an adaptive fuel
multiplier for each of the port and the direct injector with a
correction factor based on a common error in airflow to both the
port and the direct injector, the common error estimated based on a
ratio of a change in air-fuel error to a change in fuel fraction
from the port and the direct injector during engine fueling; and
adjusting fueling via one or more of the port and direct fuel
injection using the adaptive fuel multipliers. In any or all of the
preceding examples, additionally or optionally, the adaptive fuel
multiplier for the port injector is based on a first ratio of the
change in air-fuel error to the change in fuel fraction from the
port injector, wherein the adaptive fuel multiplier for the direct
injector is based on a second ratio of the change in air-fuel error
to the change in fuel fraction from the direct injector, wherein
the common error is based on a minimum of the first and the second
ratio when the first and the second ratio are within a threshold of
each other, and wherein the updating includes reducing the adaptive
fuel multiplier for each of the port and the direct injector.
[0129] Furthermore, any or all of the preceding examples, may
additionally or optionally further comprise, indicating degradation
of the port fuel injector when the adjusted adaptive fuel
multiplier for the port injector is higher than a threshold;
indicating degradation of the direct fuel injector when the
adjusted adaptive fuel multiplier for the fuel injector is higher
than the threshold; and indicating engine fueling error due to the
common error when the adjusted adaptive fuel multiplier for each of
the port and the direct injector have a common directionality and
each adjusted adaptive fuel multiplier is higher than the
threshold. In any or all of the preceding examples, additionally or
optionally, the air-fuel error is based on a difference between a
commanded air-fuel ratio and an actual air-fuel ratio estimated by
the air-fuel ratio sensor, and wherein the adjusting the fueling
includes: updating the adapted fuel multiplier commanded to the
direct fuel injector while disabling the port injector responsive
to degradation of the port fuel injector; and updating the adapted
fuel multiplier commanded to the port fuel injector while disabling
the direct injector responsive to degradation of the direct fuel
injector.
[0130] Note that the example control and estimation routines
included herein can be used with various engine and/or vehicle
system configurations. The control methods and routines disclosed
herein may be stored as executable instructions in non-transitory
memory and may be carried out by the control system including the
controller in combination with the various sensors, actuators, and
other engine hardware. The specific routines described herein may
represent one or more of any number of processing strategies such
as event-driven, interrupt-driven, multi-tasking, multi-threading,
and the like. As such, various actions, operations, and/or
functions illustrated may be performed in the sequence illustrated,
in parallel, or in some cases omitted. Likewise, the order of
processing is not necessarily required to achieve the features and
advantages of the example embodiments described herein, but is
provided for ease of illustration and description. One or more of
the illustrated actions, operations and/or functions may be
repeatedly performed depending on the particular strategy being
used. Further, the described actions, operations and/or functions
may graphically represent code to be programmed into non-transitory
memory of the computer readable storage medium in the engine
control system, where the described actions are carried out by
executing the instructions in a system including the various engine
hardware components in combination with the electronic
controller.
[0131] It will be appreciated that the configurations and routines
disclosed herein are exemplary in nature, and that these specific
embodiments are not to be considered in a limiting sense, because
numerous variations are possible. For example, the above technology
can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine
types. The subject matter of the present disclosure includes all
novel and non-obvious combinations and sub-combinations of the
various systems and configurations, and other features, functions,
and/or properties disclosed herein.
[0132] The following claims particularly point out certain
combinations and sub-combinations regarded as novel and
non-obvious. These claims may refer to "an" element or "a first"
element or the equivalent thereof. Such claims should be understood
to include incorporation of one or more such elements, neither
requiring nor excluding two or more such elements. Other
combinations and sub-combinations of the disclosed features,
functions, elements, and/or properties may be claimed through
amendment of the present claims or through presentation of new
claims in this or a related application. Such claims, whether
broader, narrower, equal, or different in scope to the original
claims, also are regarded as included within the subject matter of
the present disclosure.
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